Can I get some help with this dating problem?

I’m trying, once again, to meet someone through online dating sites. My issue today is that I’m great in the writing back and forth part – with some guys – but kind of freeze up when they want to move to talking on the phone. I’m just shy about chatting on the phone with strangers; oddly enough, I have fewer problems with meeting in person. Since chatting on the phone is a logical step, can you give me any advice on how to feel more comfortable with it?