receiver of my iPhone X is not working right

My iPhone X is suddenly not working right, the receiver is so very low. I have to open the speaker to make a call. I made a reset and a restore of my iPhone and the problem still exists. I spoke to apple team and they were quite helpful and guided me on what to do. I did but still it’s malfunctioning. Is it possible that it’s a physical damage and is it under warranty or should I pay?