This app can convert any video to audio, making it a great choice for converting YouTube videos into ringtones at https://toqueparacelular.com/. It allows you to cut out any snippet you want, resize it, adjust its volume, and save it as an MP3 file. Its UI is a little cluttered, but the ringtones it produces are high quality and easy to use.

If you prefer to create your own ringtones, consider using an app like Ringtone Maker. This app is free with no in-app purchases and it supports most file formats, including MP3, WAV, AAC, AMR, and many others.