Becoming a web developer is more than just working in the browser. Web developers write applications, and you are on that path. I encourage you to continue learning PHP, and definitely continue to work with MySQL or other relational databases. But when you're comfortable, branch out to other languages and platforms and try different types of databases (for example no-SQL databases). The more exposure and experience you have to other languages and platforms, the better you'll become as a developer.
For further learning, check out the in-depth Envato Tuts+ course PHP Fundamentals.
My name is Jeremy McPeak, and from all of us here at Envato Tuts+, thanks for watching!