How to convert YouTube videos to MP3 files on my iPhone?

I know how to use the YouTube to MP3 converter online, but once it converts the video, is there a way to save it in my music app on my iPhone? (It's a 5S, in case that makes a difference.)

Youtube video downloader

I think what you need is an iPhone transfer that can help you transfer your files to your iPhone and you can enjoy your files on your iPhone. Just you need to download iPhone transfer in icoolsoft and follow the operable steps to do it.

Try this:
http://www.youtubetomp3.uno