If you can, do a video call. I find that video calls more closely mimic face-to-face communication which brings down the phone call fear.... If that's not an option, there is some advice on how to NGAF from the McGuire programme if you wanna look into that (never did that but read the book a bit). He basically recommends actively making calls every day (100/day), and stuttering through them, until you drive the fear out of you. Kinda like intense exposure therapy