You’ve gotta just go for it. Most people won’t give a shit and if it has to do with business or making an appointment, it’s really no big deal. You can even be open about it if you’re having a really tough time, they’ll usually respond with “it’s okay.” But the anxiety isn’t worth it, I know it’s difficult but there are people with social anxiety that don’t stutter that avoid the phone too, it’s best to own your stutter if you need to make a call. No simple answers though.