I used to be terrible on the phone, so I know that feeling of dread when you have to make a call. Years ago, I got a job that, unbeknownst to me, required a fair amount of talking on the phone. Long story short, I did get much more comfortable on the phone. I still had bad days, especially when introducing myself, but it’s easier overall. Many years ago when I was in speech therapy, they had us do practice phone calls. Maybe the same, starting with some “safe calls” would be helpful.