iphone SE call problem

[Joe6Pack]

When I call people they say my voice is muffled. During a call is the mic in the earpiece and the mic next to the camera lens both shut off? In other words, is the mic at the bottom of the home screen (the one I'm talking into) the only one receiving audio input.

I know when I turn on speakerphone the phone shuts off both the one at the bottom of the home screen and the one on the back, near the lens, but I'm not sure about normal phone calls.

Thanks.