I believe the most powerful work you can do ever, phones calls or not (when it comes to stuttering) isn't trying to be better at something, but rather to find out why you aren't natural in that environment already. Because the truth is, if Noone was on the other side of the phone call, we wouldn't stutter or we would stutter very very minimally. So my question to you is, Why do you feel you get put into a more panic state when one the phone with certain people?