PHP is an awesome language. It doesn't really matter what you learn first, you can always learn the rules of another language when you learn it.
Java is a great language to learn next. It's interpreted and can be used for both web and non-web applications. It's very similar to C++ in syntax as well. Learning Java has helped me to understand PHP and all other programming languages, actually.
But like I said, it doesn't matter the order in which you learn a language. I love PHP and think it's very useful!