Do you want to get access to advanced PHP tutorials? What do you want to profile in over the next few years?
The first two years of PHP development have already taught you the basics of web development with PHP. This includes syntax, basic problem-solving, tackling specific issues with programming code, probably general debugging principles and the like.
If you haven’t been exposed to other programming languages and paradigms previously, it will be a good idea to expand on best practices applicable to all sorts of web projects. Mukesh Chapagain has already mentioned design patterns – which are important for building the right project architecture for larger platforms.
Performance and security are two interesting areas to tackle. This may lead to consulting services or specialization in any of those areas in the long run.
Learning a couple more frameworks – or even web programming languages – may be a good side activity to get involved with. Laravel, Symfony, Zend Framework have innovated a lot in the PHP space. You can learn a lot about modular development, ORM for database management, migration schemas, different MVC techniques for problem-solving, lazy model loading and more.
In other words, there aren’t specific “advanced PHP tutorials” since you already cover the basics and can handle general development work. You need to push forward, take on more complex challenges and expand your area of expertise across other areas of the stack (which may very well include server administration or DevOps, among others).