Well, I am not the author, but I did review the book, so I think I can answer that. It does assume a bit of PHP knowledge. But the book does show you how to get PHP up and running so the server side code can be copy and paste and run. No fancy deployment stratagies with PHP, fortunately.
As one of the authors I can tell you that the focus in this book is mainly on AJAX as a technology where PHP represents only the supporting language for the server side of each example in the book.
The book has a complete tutorial on how to set up your working environment and chapter 3 "Server-Side Techniques with PHP and MySQL" completes the theory foundation by presenting how to create smart servers to interact with your AJAX client. You learn various techniques for implementing common tasks, including handling security and error handling problems.
A minimal knowledge of PHP as a programming language is assumed. Nevertheless, you can easily observe that the PHP techniques involved throughout the book are very well documented and can be easily assimilated.