tiny blue light at top of iPhone (front)?

I recently shattered my IPhone 6 screen and the next day took it to the mall to get it fixed. I paid $145 at a store in my mall who apparently specializes in fixing screens. When I went to pick my phone up I realized a small blue (dot) light at the top of my phone a little to the right above the camera. I asked the man what it was and he just said it was a sensor but wouldn't really specify for what.. My boyfriend is freaking out saying its some sort of monitor or something and the Apple Store cant tell me anything since I took the phone to a 3rd party place. Does anyone know what this might be??? Could it be some sketchy tracker or some sort?