I'm M/60. If phone calls are hard then make more phone calls (like a LOT more phone calls). Record yourself making the calls and listen to the recording. It's often not as bad as you think. I haven't recorded myself for about 20 years now but I remember it having a very positive effect on my fluency levels. Call businesses and enquire about something, restaurants, anything really just get creative. Make lots of calls in a row though, don't just do a few. I'm telling you the more you do it the less of a bogeyman it will be. If introducing yourself is difficult then be sure to say your name at the start of each call. It can be very hard to do at first I know but seen as you have good fluency in other areas I think it will get you past this particular problem. I used to dread making calls, it was my worst fluency situation. What I mention here has worked for me. Good luck and get busy!