My reason for not taking calls has nothing to do with anxiety. If anything, in my regular job, I am on the phone the entire time, so am entirely comfortable with talking to strangers on the phone. But, I just find a phone call would bring absolutely nothing other than a chance for me to end up in a conversation I do not want with someone I would never consent to see - not listing my phone number automatically screens out a large number of men who haven't read my website properly/I would never consent to see anyway.
I only take advance bookings by which I mean a week plus. New clients contact me via a contact form on my website or by email. The contact form has to be completed in a certain way otherwise it will not send, so unless a man fills it in precisely, he will not make contact with me. Email brings a mixed bag, and anyone who doesn't supply the requested information is ignored. Mostly those who send emails are time wasters or looking for wank fodder, so easily deleted and forgotten about.
The men I see are time poor and busy, often not even in the same country, so contact by phone isn't straightforward anyway. A email is simplistic and easy for us both, many are grateful that my booking process is so streamlined as I clearly lay out what information I need, not just for our meeting, but what screening details they need to provide, which they do. In most instances, the whole process takes 2-3 emails tops. Easy. Written comms only is the way I have always made arrangements and hasn't failed me yet. My way works for me and that's all I need to be concerned about.