Tips for syncing custom ringtones for iPhone
sometimes, you may have problem syncing your custom ringtones to iPhone, well, here are some useful tips for you.
First, make sure that:
Ringtones play in iTunes and are .m4r format
They do show up under sounds
They show up under the ringtones tab
They are in the ringtone section of iTunes under library
Second, if the ringtone is in iTunes and not appearing on your iPhone after a successful sync, make sure that none of the song fields (song name, artist, composer, etc) have special characters (like quotes, for example iPhone-Ringtone the"-" will cause the problem).
Third, The Length of your ringtone. Although they show up in the ringtones on your iPhone in iTunes after successfully syncing to your iPhone, they will not appear in the custom ringtones section on your iPhone if they are longer than 30 seconds.
If all this don't work for you, check the original source, you can find more:
How to Sync iPhone Ringtone on Mac - Apple TV Wiki