Sorry that you were offended by my attempt at humor. But of course, I had no way of knowing you didn't mean the hardware switch. This screen should not be active when you hold the phone up to your head. As Katana-San speculates, it sounds as if there is an issue with your proximity sensor. I would start by removing any case and screen protector and see if the screen does what it should do, which is go black. You can test this by making a call, any call. Then, once the call connects, hold your hand over the top of the phone, near the earpiece. If the proximity sensor is working, the screen will go black. If it doesn't, you should contact Apple and see about having them evaluate it. They can do some diagnostics remotely.
Genius Bar Reservation and Apple Support Options - Apple