Hi
I always cough after a minute or so on the phone. I have vasomotor rhinitus which means I cough under certain situations, cold, smoke, air fresheners, certain foods etc., and on the phone. If you have discovered why this happens, I,d be grateful for your thoughts.
This might be related to the way in which you use your voice when you're on the phone. You might try a few sessions of voice therapy. A good voice therapist will be able to discover what you're doing with your voice when you're talking on the phone. He/she will be able to retrain you to speak more normally when on the phone. You may be straining your voice without realizing it.