Easy way to tell is just to track your CPU and GPU usage while gaming
An easy enough way to do that on Windows with the Gaming Dashboard (win+G) - you can pin a small tracker of CPU %/GPU %/FPS discretely somewhere and keep an eye on it. If you experience any FPS loss, check which (if either) of those is hitting 100%. If you’re regularly hitting 100% CPU usage, then it may be time for an upgrade.
That said, modern gaming is rarely CPU limited. I’ve got a 3070 and a midrange CPU from… The other guys, circa 2020… And have never once been CPU throttled while gaming. YMMV, however.
Phones these days, internally, are very drop resistant - you need to be most careful about the screen and camera lense. I’m not an iPhone expert but my guess is the most sensitive things internally are the speakers and microphones, which are pretty easy to test.
Keep an eye on it and try not to drop it, but if your aren’t seeing much of any cosmetic damage, I wouldn’t stress too hard about the internals.