Don't get me wrong, if you need to do one small thing, like for example I had a desktop app and the user could submit feedback directly from the app, then a single PHP file was enough for this case(no dependencies, no frameworks), you get the submitted data, clean it and put it in the database or submit it to a third-party API that can handle it.
You will probably hear that you should use Laravel or similar. I'd argue it's a pretty big hammer, so don't reach for it if you don't need it.
The biggest issue is probably still the breadth and inconsistency of the standard library. Too many ways to do the same thing. Also, the general issues of a dynamically typed language, sprinkled in with things like == vs ===.
I like the books this guy writes: https://github.com/codeguy