Phone App-problem with 1 while in call

Using the phone app, I make a phone call (like to my service provider) and during the call, when I want to press keys to enter information (e.g. my order number) I cannot press the "1" key. I attempt to hide keypad and then re-open the keypad but I cannot get the "1" button to work. There are two things the phone does when pressing the "1" key: Most often, the screen will go blank and second most often it literally does nothing - as if I hadn't pressed any number key at all. I notice that if I put the phone up to my face and then attempt to press the "1" key, after about 10 times of doing this, it sometimes will recognize I pressed the "1" key.

I am using 6.0.1 on ATT with a 4S

Thank you,

Kurt