PHP was one of the original back-end programming languages for the web. As such, there’s a lot of less-than-perfect PHP run websites out there and a lot of them need fixing or enhancing.
All of this will require PHP version 7, which might be a problem if you have to work on older PHP versions.
It expects a VM with all sorts of goodies installed and available and we have to codify that installation. Some of this stuff is for building and some of it is for running, and the distinction between the two is blurred.