Use your knowledge to build the PHP track itself
Create Test Runners that have the single responsibility of taking a solution, running all tests and returning a standardized output.
Build an Analyzer for PHP: Exercism's analyzers automatically assess student's submissions and provide mentor-style commentary.
Build a Representer: a bit of code that has the single responsibility of taking a solution and returning a normalized representation of it.
Practice Exercises are exercises designed to allow students to solve an arbitrary problem, with the aim of them making use of the concepts they have learned so far.