A custom audio file cannot simply be selected from Files as an iPhone ringtone. It must be added in a ringtone-compatible way, such as creating a ringtone with GarageBand or obtaining one through an Apple-supported ringtone source.
- If you already have an unprotected audio file, open or import it into GarageBand.
- Trim the project to the portion you want to use.
- Return to My Songs, touch and hold the project, then choose Share > Ringtone.
- Name the ringtone and export it.
- Choose it immediately or later under Settings > Sounds & Haptics.
Subscription-streaming tracks with usage restrictions generally cannot be exported as custom ringtones.