PHP's type system is so "dynamic" that it is very easy to build frameworks for it.

For instance, PHP allows for even function calls like this:

$language = "German";

$functionName = $language."_send_email";

$functionName("Mike", "mike_1@gmail.", "Text ...");

This sort of flexibility has its own problems and it is only possible because of the very lax type system of PHP but it is also extremely powerful when it comes to developing reusable frameworks.