I started my career as a developer by learning PHP over a decade ago, it's still the language I know best, and I was even Zend certified at one point, but I don't describe myself as a "PHP dev," and neither should you. You're a developer, and most of your experience is in PHP. It's a subtle, but important difference.
I'm going to advise you to diversify your skillset, but first, if you really want to stay within the PHP world, find an agency (or start your own) that does a lot of work with either Drupal or Wordpress. They're not corporate, and there are plenty of them.
If you really want to get "unstuck," learn something new. Here's what you're going to do: find a hackathon that takes place a month from now (see http://www.hackathon.io/ or ask Uncle Google), and register for it. Then spend the next month learning Android, AngularJS, Backbone.js, Python, Rails, or whatever your hackathon is based on, and then go to the event and use it.
Given that you already have a job as a developer, there's no reason for you to be unemployable, ever. If you have a corporate job now, I have a hard time imagining that you don't have some slack in your day that you could devote to trying out Android or AngularJS, as julianpye suggested; or Backbone.js, or Python, or Rails, or whatever. If you can't find the time at work, throw your TV off the roof of your house/apartment building and spend an hour or two on it at night.
Come back next month and if you're still stuck, post again and we'll talk. (But I'm pretty sure you won't be stuck.)