The important distinction is that a phone running a server app is a small network service, not merely a storage device. That creates useful flexibility, but also security, reliability, software-maintenance, and battery considerations that a flash drive largely avoids.
Start with the job, not the gadget
A USB flash drive remains the most direct answer when files need to move between devices in person, without a Wi-Fi network or server configuration. Current mobile file-management support also means removable storage is not an obsolete phone accessory. Files by Google supports browsing, copying, moving, renaming, and deleting content on connected USB storage on Android 7.0 and later. Apple’s Files app can access compatible USB drives and SD-card readers connected to an iPhone.
That makes a flash drive particularly sensible for a one-time handoff, a travel kit, an offline recovery bundle, or copying data to a machine that should not join a local network. It has no app to keep alive, no IP address to locate, and no server credentials to manage.
An old phone becomes appealing in a different set of circumstances:
- A group of devices needs access to the same selected files over local Wi-Fi.
- The files are updated often, and reconnecting physical storage is tedious.
- The phone has enough internal storage, or a supported microSD expansion option, for the intended library.
- The owner is prepared to treat it as a device that needs updates, access controls, and periodic checks.
In other words, the phone is complementary to removable storage. It trades the directness of USB for wireless reach and the ability to serve more than one machine.
Android: use SFTP, not ordinary FTP
On Android, Primitive FTPd is one route to sharing files without root access. Its documented capabilities include FTP, optional encrypted SFTP, SFTP public-key authentication, anonymous login, and storage access through Android’s Storage Access Framework.
The protocol choice is the first and most consequential decision. Standard FTP is not made secure merely by setting a username and password. Standard FTP transmits passwords, control information, and file data without encryption. On a shared or untrusted network, that is an unacceptable default for private documents or any account whose password might be reused.
A security-focused setup should therefore choose SFTP with authenticated access. Primitive FTPd supports SFTP encryption and public-key authentication, so those features are a materially better foundation than a plain FTP server or anonymous sharing. Anonymous access is useful only for deliberately public, low-risk material on a controlled network; it should not be treated as a convenience switch for a folder containing personal files.
The practical lesson for Windows users is straightforward: do not select an FTP setup simply because it appears easy to configure. First decide which folder is actually necessary to share, then expose only that folder, and use the encrypted SFTP option. Keep credentials distinct from important personal passwords. Public-key authentication can further reduce reliance on passwords, although the supplied documentation confirms the capability rather than a particular file-path or interface procedure for configuring it.
This narrower approach also reduces the consequences of a mistake. A retired phone should not automatically become a wireless window into every file it contains. Photos, downloads, archived credentials, and app data are not all equal. A dedicated exchange folder or a deliberately curated library is easier to audit and easier to remove from service later.
Android storage permissions are a real limitation
The phrase “share your SD card” conceals an Android permission issue. On storage managed through the Storage Access Framework, selecting the root of an SD card is not a dependable way to establish lasting write access. Primitive FTPd’s documentation warns that such permission can be temporary or revoked; selecting a directory is the documented baseline.
That changes the recommended design. Instead of aiming to export an entire SD card, create and select a specific directory intended for sharing. This is more predictable and generally safer, because it limits what the service can expose. Broad all-files access may be needed when access to all files is genuinely required, but it is not a universal Android 11-and-later setup step and should not be granted casually when a narrower folder will do.
Storage expansion itself also needs a device-specific check. Not every old phone has a microSD slot. Samsung explicitly notes that not all of its devices support microSD cards, and its Galaxy S24 series has no expandable microSD storage. Older Android hardware may support it, but “old” is not proof of a card slot, supported capacity, or suitable card condition. Internal storage may be enough for a document repository even when it is not enough for a large media archive.
A configured server is not necessarily an always-on server
The greatest practical weakness of using a phone as a file server is availability. Android may close background apps, and Primitive FTPd documents that its server can be stopped by Android background-process management. A setup can work perfectly in a test and still be unavailable later when the phone has been idle.
That makes an old phone a better fit for occasional or attended sharing than for an assumed 24/7 service. Before relying on it, test the actual pattern that matters: lock the phone, leave it idle for a meaningful period, then try to reach the selected files from Windows. Repeat after a restart and after the phone has been off a charger. If it only works while the screen is active or immediately after launching the app, it is not a dependable replacement for a NAS or a conventional always-on server.
This limitation also affects backup planning. A typical single-phone, single-storage configuration should be treated as one copy of data, not as redundancy. It can distribute files, but it does not by itself protect them from accidental deletion, device failure, or a lost phone. Keep another copy of anything important elsewhere.
Software version matters too. A disclosed Primitive FTPd issue affected versions through 8.1: unprotected exported components could allow another installed app to start or stop its FTP or SFTP server. The advisory lists version 8.2 as patched. Because the server binds to network interfaces by default in the described issue, the update status is not an academic detail. Verify the installed version before using the app as a network endpoint, and do not assume an old phone’s apps remain secure simply because the phone itself is no longer used daily.
Constant charging needs nuance, not folklore
A stationary phone server may need external power, but claims that leaving a phone connected will inevitably destroy its battery or make it swell go beyond the available evidence. Apple says an iPhone stops charging when full and can safely remain connected overnight. At the same time, lithium-ion batteries chemically age, and charging heat can reduce lifespan.
The sensible conclusion is conditional rather than absolute. An old device running warm in an enclosed space deserves attention; heat and an already degraded battery are practical concerns. But permanent connection alone is not proof that failure is inevitable. Place the phone where it can shed heat, inspect it periodically, and stop using it if there are signs of physical battery damage. Do not build a valuable-file workflow around the assumption that a retired battery will remain healthy indefinitely.
Windows has a simpler option for one paired Android phone
If the actual need is simply moving files between one Windows 11 PC and one compatible Android phone, running FTP, SFTP, SMB, or WebDAV may be unnecessary. Microsoft’s Link to Windows integration can expose a paired Android phone’s folders and files in File Explorer for wireless browsing, copying, moving, renaming, and deleting.
This is a notably different model from hosting a general-purpose local server. It is designed around a paired PC and phone, rather than offering the phone’s files to an assortment of network clients. For someone who mainly wants to drag files in File Explorer without connecting a cable, it can reduce both setup work and service exposure.
There are firm requirements: the PC must run Windows 11, the phone must run Android 11 or later, and Link to Windows must be version 1.24072.258.0 or later. File Explorer can show only one paired phone at a time. Those constraints mean the feature is not the answer for every old handset or multi-device household, but it should be evaluated before deploying a separate server solely for PC-to-phone transfers.
iPhone and iPad: WebDAV works, but Windows has a caveat
The iPhone and iPad route in the supplied evidence is Documents by Readdle. Its instructions describe starting a WebDAV server, creating credentials, and mounting the device using its IP address as a network drive from Windows. This can make selected files on an iOS or iPadOS device available across the local network.
However, it should not be presented as a zero-effort, future-proof File Explorer feature. Microsoft lists the Windows WebClient service, which provides WebDAV functionality, as deprecated; Microsoft also says deprecated features are no longer actively developed and could be removed in a future update. The service does not start by default.
The result is a useful but qualified option. It may be appropriate for a local workflow that has been tested on the specific Windows installation, particularly when Documents is already part of the user’s file workflow. It is not evidence that every Windows PC will connect effortlessly forever, nor does it mean the whole iPhone filesystem is exposed. The documented process is app-based and requires the WebDAV server to be started.
Be wary of feature lists and “free” alternatives
Apps that advertise many protocols can be tempting. Servers Ultimate advertises FTP, SFTP, SMB/CIFS, SSH, and WebDAV support, which sounds ideal for matching whichever client a household already uses. Its current Google Play listing, however, describes a seven-day trial, a two-server limit during that trial, and a last listed update date of February 6, 2020.
Those facts do not by themselves prove it is unusable. They do mean it should not be treated as a straightforward, current, free substitute without independent testing. A long protocol list is less valuable than a maintained application, a protocol that protects data in transit, and a workflow that survives ordinary phone idle behavior.
A practical decision rule
Choose a USB drive when simplicity, physical control, or offline transfer matters most. Choose Link to Windows when one Windows 11 PC and one compatible Android phone simply need wireless File Explorer access. Choose an Android SFTP server when multiple local devices need a deliberately limited shared folder and you are willing to maintain it. Consider iOS WebDAV through Documents when its app-based workflow fits, while recognizing the uncertainty created by Windows’ deprecated WebClient service.
An old phone can be a capable portable local file server, but its strength is convenience within a defined network workflow—not superiority over a flash drive in every situation. The reliable version of the idea is modest: share only what is needed, encrypt the connection, confirm the app is patched, test whether the phone stays reachable, and retain an independent copy of important data.