I definitely have trouble talking on the phone. What helps me is to be in a room by myself and pacing back and forth. When I did speech therapy they had me make some practice phone calls to clothing stores and restaurants. I cried before the first few calls, but it really did help to practice and I realized that most people are relatively patient. Another stutterer I know (who is also a SLP) told me that he practiced saying his name on the phone by calling bars and asking for himself. This was back before cell phones :) but the point is that practicing while using fluency strategies can really help.