PHP has had a type system for over a decade now, including things like union and intersection types that are still not in Java. Most static checking still needs an external analyzer, but even without one, PHP does check subclasses and interface implementations for Liskov substitutability in a way that Python does not.
I know all that. The issue is that the type system only cares about classes and interfaces. It's all userland abstract types. If a type system doesn't offer safety AND efficiency (i.e. for primitives) I see no value for me. I don't see that happening.