This makes perfect sense to me. I don't know what it is about talking on the phone, but it's an extremely anxiety inducing experience for me. I'm generally fine with people, but if I have a choice of walking down the street to talk with them in person or call them on the phone, I will make the walk every time.
Best I can figure out it stems from being verbally abused as a teenager when I had a job making cold calls. People are vicious on the phone in a way they never are in person. Some people seem to use strangers on the phone as an opportunity to safely vent whatever pent-up rage they have. And even though people are just as vicious online, it just doesn't have the same bite as it does when it's a human voice filled with rage.