What's worng with my IPhone 5?

When I recorded a video and played it, I could nearly hear the sound, and I did many tests but they all had the same result: the audio is very low. What's wrong with the speakers and how could I fix it. I think this also has to do with when I make a phone call, the other person can't seem to hear me.

Probably the iphone's mic is faulty. Try using the external mic, or headset.

I would return and see if they will fix it because this problem may happen during calls.