This happens to me quite often as well, too. I could be speaking perfectly fine with a coworker and then the phone rings, and an immediate vocal block happens when I try to say hello. It's to the point where the person on the other end thinks something is wrong with our phone connection. I work in a glorified call center for reference so some days it's awful, but most days are fine. I usually end up stressing crying on the drive home, lol. I wish I had a solution for you, OP, but I guess I'm really just commenting to let you know you're not alone. A lot of us experience this and identify with your frustration.