To clarify, my question was about resources that are helpful for learning PHP specifically for Rails developers. These are different to resources that are helpful for learning PHP, but not specifically for Rails developers.
The two are quite easy to tell apart. One set builds on existing knowledge a Rails developer will have. These are likely to have low Google rankings, because more people learn PHP and then learn Rails, not the other way around.
An example would be http://railsforphp.com/reference - an easy-to-use side-by-side Rails and PHP reference that works almost equally well in both directions. (this particular example however is easy to find on google, being intended for the more numerous PHP developers learning Rails, so most people interested in this topic will probably already have found it)
The other set doesn't build on existing Rails knowledge. These are less niche and can easily be found using google.
To further clarify, this thread is aimed towards people with interest or experience in learning PHP having previously learnt Rails. Hence the title, "Learning PHP for Rails developers?".
This thread is not aimed towards for trolls, or people who are not interested in the topic "Learning PHP for Rails developers". The clue here is in the title, which, helpfully, is "Learning PHP for Rails developers?". http://lmgtfy.com/?q=Basic+communication+skills