What is preventing me from hearing any audio source other than using the phone as a phone?

I have an iPhone XS running 15.3.1 although the problem described predates the upgrade. I can hear the phone fine when I'm on a call but when I try to access something like You-Tube or some clip that someone sends me, there is no sound whatsoever, no matter how many times I hit the un-mute button. I'm wondering if this is because I am not signed into Google, but even when I manage find a site that is not a part of Google there still is no volume. Baffling. The phone, as a phone, works great, volume sliders work etc. Any ideas? Thanks!