I used to have major issues with answering the phone. My rule about that for myself was to answer the phone as soon as it began ringing, no matter what. That way, not matter how uncomfortable I felt, I was forced to interact with whoever it was on the line. It was hard, but once I got in the habit of always answering the phone, it got a little easier. I also pretend that I'm acting sometimes, and I pretend to be some hypothetical confident, outgoing person who knows how to be friendly with strangers.