How to download youtube videos on to my iphone4s?

I recently got a new iphone but I lost all my photos and videos because I transferred sims! I found out how to get the photos back, but I'm having trouble with my videos. I know how to download youtube videos onto my computer, but I was just wondering, how do you download the videos on to your phone through itunes? I've done this a few years ago by uploading it to youtube and then downloading and transferring to my phone but I just forget now. Also, the itune is different. So does anyone know how?

You can download them in your computer using the VDownloader, and then sync using iTunes!

I do it all the time.