How to Set a Custom Ringtone on iPhone
Save the downloaded MP3 in Files, import it into GarageBand, then export and assign the ringtone using Apple's documented workflow.
iPhone ringtones can be up to 30 seconds. MP3 playback and download stay available; after an eligible MP3 succeeds, its signed-in owner can explicitly request asynchronous M4R preparation and download the M4R only when ready. Neither download installs a ringtone.
Read the complete iPhone ringtone setup guide
