I am surprised no body has mentioned Exercism yet. Go to exercism.io and there are around 60 problems for PHP that you can start working on it. The good part is

I am surprised no body has mentioned Exercism yet. Go to exercism.io and there are around 60 problems for PHP that you can start working on it. The good part is, it has tests built into it. You can gradually work on a solution by progressive approach and thus passing each test successively.