Are you talking about to the left of the speaker you put your ear on? Where the two dot things are? I'm wondering if it's infrared and you can somehow see it? There's a proximity sensor to see if your face is against the screen, to turn off the screen.
One of the holes is the prox sensor that turns off the display when u r on a phone call and the other hole is the light sensor that controls your brightness when that setting is in auto mode