Does your manager(s) know about your stutter? I mean it sucks, but some tasks just aren't suited for stutterers, like answering phones or speaking over a microphone. Blocks can be very transient. What I could say easily last week, I might not next week. Generally (for some of us) the more you say something and feel anxiety over it, the more likely you are to have a block. Take names, for instance. I knew a stutterer who legally changed his name to something easy to say. A year later, he stuttered on the new name so badly that he had to have it changed again. Just be practical. Without formal speech therapy, your options are to A.) leave positions where you're having frequent fluency trouble, or B.) allow yourself to have fluency trouble and learn to be okay with it. Like they say, instead of trying to not stutter at all, try to stutter better. Most of us will never be 100% fluent, but by accepting our disfluencies we can rid ourselves of a lot of the anxiety which exacerbates it.