Why doesn't my phone play videos that I have transferred from my computer?

My phone is a Motorola Razr 2 v9, I used the free Youtube Downloader program to download from Youtube a couple of music videos and the like to my computer in a .3gp format, however when I copied them to my phone then accessed my phone, they didn't show up in the video section at all, and some of them only showed up in the music section. Anyone have a clue whats wrong?