Hi @Anonymous and Welcome to the Community Forum.
I'm sorry to hear of the issue with the iPhone.
May I ask have you checked the speakers and ports for dust / lint.
Applied any screen shields recently.
The volume is turned up using the side + volume button.
Also try Holding the Top Button and Home Button until the Apple Logo appears, and then let go of both.
Your iPhone will reset.
And or ;
Settings , General , Reset , Reset All Settings.
Good luck and please let us know how you get on.