Thanks for reaching out in Apple Support Communites. I understand that you're trying to remove a ringtone that you created using the GarageBand app on your iPhone. I know it's important to be able to manage the content on your iPhone and I can assist you. In order to do this you'll want to re-install the GarageBand app from the App Store and then follow the instructions below:
GarageBand for iOS (iPhone, iPod touch): Share GarageBand songsManage exported GarageBand ringtones
In the My Songs browser, tap the Select button, then tap a song (or touch and hold a song).
Tap the Share button
, then tap Export Song As Ringtone.
The Export Ringtone panel opens.
Tap Your Ringtones.
A window opens showing all previously exported ringtones.
To delete existing ringtones, do one of the following:
Tap Select, then tap the Delete button for any ringtone you want to delete.
Swipe a ringtone in the list, then tap its Delete button.
When you are finished, tap Done.
To return to the Export Ringtone panel without deleting ringtones (or if there are no existing ringtones), tap Export Ringtone.
Once you've removed the ringtones you can delete the GarageBand app from your iPhone.
Happy Holidays.