Well first of all calm down. Its no big deal. It was only one phone call. Relax. Now my advice would be to go to a speech therapist if this continues to bother you. I used to have a severe stutter during school (everyday humiliation) and hell I stutter even now. I searched everywhere on the internet and saw dozens of videos but none were of any help honestly. Finally I went to a therapist after finishing school and my stuttering is down 70%. It really has helped a lot in my life.