[jiggy2011]

PHP5 has real type hinting in the language, so you don't need to write any more than you would in Java.

[TazeTSchnitzel]

And soon it'll even have return typing, should that RFC pass.

[Rapzid]

phpdoc handles much more than just typing function parameters.

[debaserab2]

By far the most common usage is parameters and return values. Even moreso than comments.