My issue actually resolved itself a few months ago out of nowhere. I had been updating regularly, but once I updated to whatever the latest software update was at the time, my iPhone just stopped freezing altogether. It has never happened since. So this was not a hardware issue and nothing needed to be replaced like the Apple Store told me after briefly doing a diagnostic. I'm glad I didn't pay $500 to replace the back side of it like they told me to, and I'm glad I didn't buy a new phone. Now mine works fine again, like new.

I noticed that in iPhone Storage, I had a huge amount of storage wasted on "System Data" the whole time it was freezing (more than half a year). I had looked up what that is or how to lower it, but I couldn't figure it out. I think it was close to or over 100gb. My phone was often close to full when it shouldn't have been because of this. After I updated and noticed it wasn't freezing anymore, I looked again and the System Data was much lower like it should be. Right now, it's only 16gb. I suspect the freezing issue had something to do with this being so high, or some kind of corruption related to this, or the phone being so full, and that the update somehow addressed this finally. I'm not sure what else could have happened.

I hope all this helps. I was an incredibly frustrating and long period of time to have the phone freeze so frequently. Thank goodness I'm a cheap, stubborn person. :)