Do you block and have avoidance behaviors(switching words, avoiding eye contact, avoiding conversations, etc? those things are almost entirely due to anticipation anxiety. Unfortunately, the way to address the issue and get *lasting positive results* is to basically do the thing you are scared of. Let others hear you having repetitions or prolongations. Start by doing it in mirror, alone, making eye contact with yourself, and do brief, voluntary repetitions. Build up to phone calls and in person as you are able to. When talking to people, disclosing is extremely helpful for many many people. Make eye contact, begin speaking slowly and on an exhale. I find that enunciating with interesting tone, cadence also helps enormously.