How to set an MP3 as a ringtone on Android:
Apple only allows users to customize unique ringtones for iPhone by making a ringtone from an MP3 file. You cannot automatically add MP3 files to iPhone, then set as ringtones.
Although several steps are involved, and they require some attention to detail, the process goes fairly quickly.
Open Apple Music, choose Music > Preferences, click Files > Import Settings. Choose the encoding format M4R and click OK. Pick the audio files and click Convert. It will begin converting MP3 audio to M4R ringtone format for iPhone.
Use tones and ringtones with your iPhone, iPad, or iPod touch
How to Set Ringtones on iPhone? After adding the M4R files to your iPhone, you can set them as ringtones for your iPhone. All you have to do is go to “Settings” > “Sounds”, and choose the ringtones for the call and the messages respectively.
Related. You can turn your Mac or PC into your own ringtone maker, creating custom ringtones for your iPhone, from almost any MP3 file. Using Apple's free iTunes software, you can edit and convert an MP3 to an iTunes ringtone for the iPhone.
Set an MP3 file as a ringtone by going to Settings > Sound & vibration > Phone ringtone > My Sounds. Select the + button, find the MP3 you want to set as a ringtone, select it, and hit Save.
Open Music Converter for Spotify on your Mac or Windows. Then it will load the Spotify app automatically. Find any song or playlist that you'd like to make as iPhone ringtone, and drag it into the ViWizard conversion window. Or you can copy and paste the music link to the search bar and click "+" icon.
To set a song the custom ringtone on iPhone XR:
Bonus Tip: How to Custom Ringtone on iPhone 12
Go to Settings > Sounds & Haptics (on supported models) or Sounds (other models). Tap Text Tone, then do one of the following: Tap Vibration, then choose an option. Tap a sound below Alert Tones.