Maybe a big key in overcoming it is “resisting time pressure.” You become anxious when you first pick up the phone and it causes you to wanna rush, which then increases your anxiety more. Instead, have the mindset of, “I’ll talk when I feel comfortable talking because it’s my turn to talk.” So when you answer the phone, instead of immediately starting to talk, take a deep breath, relax your muscles on the exhale, and hear the other person’s voice say hello and become comfortable with their voice. Then begin to talk. Basically you are pausing on purpose so that you don’t rush and so that you take back control of your anxiety. Does this make sense?