Congratulations on your book! I have an idea of how long it takes to push something of this size out, so you must be happy to be finally done with. Though, to be honest, this is only the beginning. For books, marketing is >50% of the work. Below are some pointers/advice.
1/ Do you have a webpage for your book? I think that can make a big difference in the conversation with your potential readers. Here is a sampling of some "book pages" out there:
http://nathanbarry.com/webapps/ (Nathan's)
https://django.2scoops.org/ (Danny's)
http://minireference.com/launch40 (mine)
2/ As aparadja said, a blog will also help people find you. Getting traffic via AdWords is expensive, whereas organic search is free. You can release parts of the book, or even better develop new content --- I'm sure there are some things which you didn't get to. Now's the time ;) The big picture is this: you have a unique expertise and experience using PHP on the server-side so many people will be interested to hear about your experience and your opinions about what is happening in that domain.
3/ Did you get a professional copy-editor to go through the text? I recommend you use the first $1k of profits and hire someone to proofread the book for you. It cannot be a friend, friends will only encourage you and say "great job," but a professional editor will be able to give you critical feedback about which sections need more explanations or rewording. Typos are also a nightmare (both English and code-wise). If a reader sees a typo on every page or two, he/she will quickly lose trust in you, and you don't want that.
4/ You should also consider offering your book in print (through lulu.com for example, or lightning source). Self-published print sales can be very interesting, I know eBooks and iPads are the craze, but #PrintNotDead https://twitter.com/minireference/statuses/40222755949812940...
Good luck, and feel free to get in touch with me if you would like to discuss further.