"Do not use getters and setters" looks like a hastily advise, but its meaning is very important and it is "do not break encapsulation", which moves us to the question what the encapsulation is.

He notes that encapsulation is, in essence, hiding parts of the code away so that the user/other coders only see a little bit of the magic that happens. He argues that getters and setters are a valid part of the encapsulation process and that designing a good, easy to use system almost requires them.

Today most of the popular programming languages support objects, limiting scope, modularity, passing by value, and sophisticated built-in types. There should be no reason to deliberately expose an object's data to the rest of the code because the language can enforce encapsulation and data hiding.

While not specific to PHP, the post does recommend against them because of one simple reason common to all languages that make them possible - they "break the encapsulation OOP offers". For them, they're like a cheat to get around bad coding practices and are not needed to make a successful application work.