Its weird to me that in the age where people live their lives through smartphones, that nobody in those 5 minutes had one? I carry mine to the gym, either in my pocket or in my locker?
Obviously the guy should have phoned 911 immediately, but if someone fails to act, it is your job to act, not wait around. He could have frozen up, not believed them or quite frankly just did not know what to do, it happens in these situations.
Perhaps the real story is that he did not dare enter the ladies locker room, regardless of who had a phone or what the details are.