This seems to have helped the issue for me.. it will tell you online that in iPhone settings, under music, the equaliser (EQ) only applies when playing Apple Music. However I swear that this is not the case on this phone as if you put the equaliser onto almost any setting it will distort on a lot of other platforms or channels too as they are possibly already compressed to maximum levels and then any tinkering with the sound causes distortion. The solution that I have found is to set that equaliser to off or flat when not playing music. Try it out, see if it works for you. It seems to be some weird glitch where the equaliser settings now apply across almost the whole phone. I think this is responsible for the horrendous and unbearable distortion particularly on things like YouTube videos with a lot of spoken word content. Anyway, this kind of worked for me, after a lot of playing about as the audio quality was horrendous until I did this. Now it’s way better, but I wish Apple had bothered to find this out/explain this…