It's a fine backend language for a small to medium sized website, but you need to be aware that at a certain size (in terms of complexity of the application you are building) you'll often find yourself fighting against the language. That's not to say you can't build large applications in PHP, just that you need a great deal of discipline to do so. You'll either need to adopt one of the MVC frameworks (Symfony for example) or roll your own. A lot of the features in the framework you chose will be workarounds for limitations in PHP itself (such as its lack of decent namespacing and poorly designed database access primitives).