Do you have a private area or an office? I find pacing around the room helps me Also they cannot see your face. In speech therapy I was told to try and not use “secondary movements” to help with your stutter because sometimes it looks bad an uncomfortable. However I find when I distort my face and flex random muscles or move my head in a certain way then I can get the word out As they cannot see you on the phone then I’d just use these secondary movements to ur advantage