You're right that intellisense is much more complicated in a dynamically typed language like php. Consider for example
function get_foo($x) {
return $x ? new abc() : new xyz();
}
get_foo(123)->... can your IDE autocomplete here?
Don't know about PDT, but Netbeans is unable to handle this, and phped requires 'get_foo' to be annotated in a special way.
I haven't yet tried the upcoming WebIDE from Jetbrains (http://www.jetbrains.com/webide/features/index.html), but looks promising in this regard (see screenshot).