Hi, 19M from Melbourne Australia I relate to you on a deep level, as phone calls are always extremely challenging for me and make me extremely anxious. Especially with people I don't know too well, or there is a lot at stake in the phone call (boss, new job etc). Sometimes I get to the point where I elongate my words for 10 plus seconds just to get a word out. Usually it doesn't result in anything but a laugh occasionally from the person at the other end. However, this is a guttural feeling of embarrassment and anger within myself that I cannot hold a conversation on the phone without sounding nuts. I have gone mute sometimes for a little while as talking for me feels more like a labouring exercise rather than effortless communication. However, going mute has never solved my anxiety and it makes it worse. So I would never recommend a person with a stutter to go completely mute for a long period of time. I wish you the best.