I would agree with the writing down your words for the for call suggestion and the relaxation as well. But I would not recommend and of the physical suggestions. These can because learned behaviors and it will very difficult to reverse them. I know people that would tap or pinch their thighs under the table at meetings to get their words out and eventually they were punching there legs and pinching so hard they were black and blue after. I used to lean forward when I was blocking and have finally stopped that. I still contort my face a bit when I get stuck and almost cross my eyes. Unlearning this is my next challenge. Next time you are blocking on the phone or in person, try this, stop , pause and smile- then try again.