Totally get it, and phone calls are the hardest for me too. I stutter very badly on the phone. But my job also revolves around making phone calls. Had one experience recently where the person I called outright mocked me going "uh uh ooh ah ah I can't understand you." I remember early in my journalism career, I had to make phone calls in front of the other reporters in the room, and I was trying to tell someone my cell phone number so they could call me back. It was literally about 5 minutes of me trying to say my cell phone number and have the person on the phone understand me, all the while my editor is looking at me with this sympathetic grimace on her face. That was super embarrassing. Just keep pushing through it. If it helps, you can tell them off the bat you stutter so might be hard to understand.