Simultanatelephobia 

The fear of trying to call someone at the exact moment they are trying to call you, and thus being irrationally afraid to pick up the phone for fear that the party trying to reach you would receive a busy signal. This mental illness was very common before the advent of "call waiting".

The nervous bitch wouldn't let anyone use the phone because of her simultanatelephobia.

Simultanatelephobia by Alan V. February 19, 2005