It's important to remember that PHP is not going to be suitable for every situation that you develop in and knowing what else is out there, and having a basic knowledge in how the other languages work and their pros vs cons means that you can chose the right solution at the right time. Ultimately if you want to be a PHP developer I would recommend really focusing and learning that language first and then looking further afield. After all its better to be a master of one language, with the ability to pick up new skills as needed in others, than be an amateur at 10.