I work as a sign language interpreter. Primarily at a high school but secondarily at a Video Relay interpreting call center. Basically a deaf person has a camera attached to their TV, they call a hearing person (doctor, kids school, store etc etc), I see them on my screen while I'm in my little cubicle, and place the call. Then I interpret back and forth between the hearing person on the phone and the deaf person wherever they may be either from home or in a mobile device. Point being a large part of my work involves talking on the phone. How it works for me is that it's rarely ever actually me speaking my own words. I only faciliate communication between two people from different cultures and language groups. Most of the little phrases I have to say before I actually connect the call are all so rote and memorized that I can be reading something on my computer as I say it. I only stutter if I get thrown off by something and lose focus or get frazzled. Takes me a bit to get my composure again and be fluent. Now, when I'm speaking with friends, family, wife, etc in person or on the phone I always stutter. Some days better than others but it's always there. tl;dr I can speak on the phone for work because it's not my words and that for some reason works for me and I rarely stutter.