I spent about two weeks really getting to know Backbone and then another 2 months integrating it into the latest Phreeze Builder. You can use the builder utility to generate a PHP/Backbone app with just a few clicks (based on a MySQL database schema). If you aren’t interested in the Phreeze framework, I happen to think that I’ve done a decent job of organizing a Backbone app into something that you can use as an example. I’ve managed to implement things that I haven’t seen explained like pagination on collections. For the UI I went with the ubiquitous Bootstrap from Twitter (using quite a lot of the user input controls), so the layout is fairly clean. I’m not 100% satisfied but I feel like it’s a good start. The PHP part of the code is written using the Phreeze framework but essentially it’s just a standard REST API. So again if you don’t really care for Phreeze, you can at least take a look to see how your own PHP code needs to be written to work with Backbone.
If you’re interested in using Backbone.js with PHP, I’d be interested in your feedback. If you don’t want to install Phreeze you can just check out the video or play around with the Live Demo (the DB resets every hour so feel free to edit away).