Question: how to make a song on itunes a ringtone on iphone?
Answer: Open iTunes on the desktop to get started.
Choose the song you want to use to create a ringtone and click on it.
Right-click on the song and choose the Song Info option.
Click the Options tab.
Choose up to a 30-second period in the song that you'll want to make your ringtone. ... 
Click OK.