There's not really a technical fix for your phone's camera audio from concerts being distored. Usually depending on how much audio your phone's internal microphone pick up in an environmental situation determines how well both video and audio will come through. Which device do you have?
You will need to dampen the sound by using foam or fur that will control the sound waves enter the mic.
the phone by itself is too exposed to the noise at the event.
You can use a 3rd party mic accessory to record the sound, which will be your best option.
Or if you know where the mics are on the phone... you can adhere dampeners around the mic to control the sound waves hitting the mic. This will be messy and difficult to do properly and effectively.
