Phone Phobia

Well my problem I'm dealing with is answering work phones. and yes only at work i have this phobne phobia issue. I go to answer the phone and no words come out AT ALL. its almost unbelievable. i don't know how to overcome this fear. and its weird because i can answer my cell phone with no problem and even if i don't know who is calling me. its just work phones and they scare me.