I'm the same. I have social anxiety and generalised anxiety disorder and I find it very difficult to make phone calls, as well as receive them. I used to find it impossible actually. If I receive a call from an unknown number or I don't recognise the number, I panic and feel sick. I watch and wait until it stops then I immediately scour the internet to see if it was a scam call. If it's a call from work, I very rarely answer. I used to do that but I got used to answering (in my old job) after about a year. However I recently got a new job and find it hard to answer again. I let it go to voicemail and listen, then I spend about 3 hours working up the courage to ring them back. I'd rather call than answer, because by then I can work out in my head what I want to say, especially if I have listened to the voicemail and know what they were phoning me about. If it's a friend, I will usually answer. My friends don't usually call me though so it's not really an issue. BUt yeah, I totally understand you.
All I can say is it gets (slightly) better with practice. The anxiety you have when answering/making calls won't subside too much, but at least you'll be making the calls. 3 or 4 weeks ago I had a lot of people to call. My student loan hadn't gone through, and I had to call to get it sorted. I also had to call my uni and the loan company. I surprisingly got better at calling. My friend encouraged me to answer a phone call from work the other week too, and I did it. It was a HUGE step for me, to answer a call- I wasn't even in the comfort of my own place, I was out, on the street, and I answered it. I genuinely think the practice the previous week, actually helped. I still felt horrible and anxious, but I did it nevertheless. Its worse not knowing believe me.
If it's so bad that you just can't do it, maybe consult a doctor. It could be part of an anxiety disorder, or it could just be a phobia- but they still might be able to prescribe some medication. I'm on citalopram for my anxiety and I believe it's working, so if they offer some kind of treatment, maybe take it and see if it makes a difference, I know how hard it is so keep your chin up and keep trying, it's so hard but it's something we have to do as we go into adulthood. Good luck!!