How to convert a song from youtube to iphone?

I have a mac also if this helps. I used a youtube converter and converted the songs but now they will not download onto my iphone when I sync it

All you have to do is copy the youtube link and paste it when you get to the website: Snipmp3.com. My school uses it for our award winning video class at KP High, so I know the site is legit. Then just click convert, and it will ask you where you want to save the file. There you go. And thanks for answering my question btw