I used to be like that, and for the first months I'd only take bookings via e-mail, as I was always phone shy. But like sensualmilf said, it's hard to identify timewasters this way, and I was getting way too many no shows. Most of them were no shows, really.
I've since switched to phone, and although it was awkward at first, I definitely got much better at it, and after a few months it's not a problem anymore. I now get irritated at people texting me, with their stupid 'hi' and 'available?', just wasting time when they could just ring me and get done with it.
Bonus, I can now make phone calls in my private life without getting all nervous. And that is a huge plus for me.