What makes a good ringtone
The first 30 seconds of the file are already selected, with a 1 second fade in and a 2 second fade out. Move the selection to the chorus or a recognizable riff: the part has to be clear within the first second, because a call rarely rings for long. Play selection lets you check it.
An iPhone ringtone is an M4A (AAC) file with the .m4r extension and may be up to 40 seconds long, so the iPhone choice keeps the selection within 40 seconds. Android phones take ordinary MP3 files of any length.
Put the ringtone on an iPhone
With a Mac: connect the iPhone with a cable, select it in the Finder sidebar and drag the .m4r file onto the iPhone window. On Windows, use iTunes: select the iPhone and drag the file onto On My Device in the sidebar. Then choose it in Settings > Sounds & Haptics > Ringtone.
Without a computer: save the MP3 version to Files, open GarageBand, create an Audio Recorder project, import the file from the loop browser (Files tab), drag it onto a track, then in My Songs long press the project and choose Share > Ringtone. GarageBand ringtones are limited to 30 seconds. Recent iOS versions may also offer Use as Ringtone in the Share menu of the Files app; if you see it, that is the quickest way.
Put the ringtone on an Android phone
Download the MP3 on the phone, or copy it with a cable into the Ringtones folder of the internal storage. Then open Settings > Sound and vibration > Ringtone (the names differ a little between brands) and add it with the plus button or My sounds. Some file managers also offer Set as ringtone when you open the file.