The assault wouldn't be the statement over the phone. It would be during her approach, which was immediate and, given the conversation on the phone, would yield the reasonable apprehension of harmful or offensive contact. He wouldn't have that apprehension during the phone call, but he would when she enters his office.
I don't think transferred intent is an issue at all here. With transferred intent A sets out to cause harm to B instead, unintentionally, causes C to suffer the harm. All we have in this hypo are two parties so I don't see how transferred intent can apply. I believe you're better off sticking with assault.