I really enjoy this course. It not only covered the PHP package development but also covered topics beyond that.
For example, it explains the versioning, CI, style CI, importance and guide of creating a README, license file, and change log.
It helps me to get started building a package for PHP and at the same time, I can use the lessons I learn as a checklist to make sure the package is complete.
Some of the links from the lessons, I put them below for my future reference.