Its sundenly very low. And its not the plastic because there is no protecting plastic thing. What else could be the problem?
IPhone 5 incoming call volume?
Make sure the volume is up when your talking on the phone. I usually have to double check otherwise I can't hear the other person haha. I actually have a similar issue where the brightness would suddenly become low. So I just have to go back to settings and fix the brightness. But to get back on the road just make sure you have your volume and sounds up. If all else fails. Take it to apple. Or try speaker phone. Possibly the headset.