PHP itself is pretty fast. It's the things that people do in PHP that get slow. Most of the Yahoo frontends were rebuilt in PHP in 200x because it was fast enough and much more usable than the thing they used before(trigger warning: hf2k)

Of course, people then go and build up sculptures of objects that will be thrown away after every request, and that stuff makes everything slow (that style of code is why PHP wasn't good enough for Facebook, IMHO), but you can build trash sculpture in any language.