Why can my phone not read a USB flash drive?

A computer reading the drive does not establish that it is compatible with your phone. Check the connection, power needs, and the drive’s partition and file format against the instructions for your exact phone model. Avoid reformatting as a first step, since changing the drive can affect its contents.

For iPhone, Apple says external storage connects through a compatible connector or adapter and can be browsed in Files. Apple also specifies one data partition and lists supported formats including APFS, exFAT, FAT32, and FAT. [S1] These requirements should not be assumed to apply to other phone models.

Compare the drive’s plug with the phone’s port and note any adapter in between. Check that the adapter is intended for connecting external storage; a matching plug alone does not establish compatibility. For iPhone, Apple calls for a compatible connector or adapter. [S1] For other phones, consult that model’s instructions.

Also check whether the drive needs a power source. Apple notes that external hard drives often need their own power source. [S1] That note is specific to Apple’s iPhone guidance and does not mean every phone or flash drive has the same power requirement. Follow the phone and drive makers’ instructions rather than improvising a power arrangement.

Yes, the phone may not support the drive’s partition layout or file format. Check both against the requirements for your exact phone. For iPhone, Apple specifies one data partition and lists APFS, exFAT, FAT32, and FAT as supported formats for external storage. [S1] This does not establish what another phone supports or guarantee that every setup using one of those formats will work.

Before changing a partition or format, back up important files. If you do not know how to inspect the drive safely, ask someone qualified to check it without modifying it.

Try one check at a time and stop before making changes that could erase files:

1. Record the phone model, drive type, and adapter.
2. Check the phone maker’s instructions for external storage and compatible connectors or adapters.
3. Check the drive and phone instructions for power requirements.
4. Compare the drive’s partition and format with the requirements for that phone.
5. If the phone recognizes the drive, use the file-browsing app specified in the phone instructions. For iPhone, Apple says compatible external storage can be browsed in Files. [S1]
6. If it still fails, note any message shown and ask the phone or drive maker, or a qualified technician, before changing the drive.

If you need the files now, one alternative is to access them on a computer that already reads the drive, then transfer them using a method supported by both devices. Check those devices’ instructions, especially if the files are important or sensitive. The supplied Apple guidance does not identify a transfer method that works for every phone.