Just wanted to stash here many of the books read, podcasts listened to, sites visited that have helped to bring about a better sense of code design, team work and overall day to day goals.
Also check out my podcast DevelopersHangout.io
The Clean Coder by Robert Martin book is a look at being a "Professional" coder and all that comes with it. It is a great look at not only how one should be in the role of a Programmer but what to expect of each other as a team.
Domain Driven Design A great look at being a programmer that not only makes code but more importantly bridges the gap between the vision of the business with the goals of the code.
It is not about PHP directly but it all applies to good Oo PHP design patterns and thinking. There are so many classics he quotes that could be added here as well.
There are a number of great books on this as well. Right now a short and simple look at how to make an API, I think, is Build APIs You Won't Hate by Phil Sturgeon. Great code example too on Behat and API testing