Ringtones

You can't assign a purchased song as a ringtone but you can make custom ringtones using the Garage Band app.

You can create custom ringtones using your iPhone: Open the GarageBand app and find the song that you want to use to make a ringtone. Touch and hold the song, then choose Share > Ringtone. Enter a name for the ringtone, then tap Export

Use tones and ringtones with your iPhone, iPad, or iPod touch - Apple Support

Can this still be done with the new IOS? You no long sync your phone through iTunes, it's Finder now. When I got the new XR phone the other day, I wasn't able to to sync it with my old phone.......