Phone calls were (and still are to an extent) hard for me to get used to. I used to be similar to you and absolutely terrified of answering the phone or having to call someone. The only thing that did it for me was when I started applying for internships and after about the 5th phone interview I was more comfortable with them. Even then, until I started my current job, where I get random calls every now and again, that's what made the biggest difference. I totally understand that trial by fire isn't an effective solution for everyone. For me, just the fear of having to do it without actually having tried it was my biggest challenge. I hope you find something that works for you!