Doctor with stutter here. It’s neurological, the behavioral inhibition system tries to prevent you from stuttering. And of course you get anxiety from the blocking. Solution? Explain the block and that you want to say something. Then resist the time pressure and try to focus all your attention on your voice, listen to yourself and try to use your own voice to soothe yourself, keep attention on your voice so that auditory feedback to your cerebellum keeps working and stops you from blocking.