I'm in this situation as well. In an office of like 7 people and I'm probably on the phones most of the time next to HR so when I talk literally everyone can hear what I'm saying. My boss is also right behind me so it puts extra pressure on me to say the correct things as well as come off smooth and confident on the phone. I've somehow surprisingly been able to not stutter nearly as much now but I do come across a block quite often especially if Im asked my name lol. I also talk pretty low so that doesn't exactly help neither. Only really because it's so freaking quiet you can hear a pin drop. If i had my own closed off office I bet I could ace these phone calls with ease tbh