PHP is a interpreted language, and that would (normally) mean that comments have to be parsed and therefore cause a performance penalty.
However, as far as I know, PHP comes with an optimizer which compiles/converts the raw source code into some bytecode or similar, which would mean that comments get stripped out and therefore no longer affect performance at all.
Do comments affect PHP performance (no matter how tiny the impact may be) or not at all?
As far as I know, any comments for any server-side script are removed when compiled. It might take an extra .0001 milliseconds for their computer to remove that, but otherwise it doesn't do anything.