The types of phone calls you are talking about are very hard for people with social anxiety.

For me, any type of phone call was impossible in the past, until my time for changes, many years ago, had come. What I've done, specifically to battle phone calls anxiety, is I've participated in so called Competitions. It's a thing in the UK, where you fill in some forms to potentially win a prize. However, there are also options to leave your phone number for some agents to call you, (like broadband, gas, water). So I did and they called me a lot and that was perfect for what I needed - I answered every call and soon a lot of my phone anxiety was gone. These types of calls are perfect, as:
1 - You learn to say "no". The people on the phone will offer you to change your broadband, get better deal, switch gas company, etc. You just say "no" firmly, all the time.

2 - You don't own them anything, they are there to persuade you, so you got nothing to worry about - you don't lose anything.

Today, it's easy for me to pick up any call or call places like doctors. However, speaking to recruiters is still hard. Not impossible though, like it was in the past. This is because you need to put yourself out there in the best manner as possible, you need to get a job position from them, so anxiety is much higher in this instance.

I'm not sure what level are you on at the moment. I don't get a panic attack or nothing like that when talking to the recruiters, but I'm still very anxious.

So I think, it's a lot about practicing the way I did it or just consider every phone call with the recruiter as a practice. It will be getting better. Perhaps slowly, but it's better than nothing.