PHP Dev wants to learn a framework Symphony or Rails?
What framework is better what is the growth opportunity? Stick with PHP or move to Ruby/Rails ?
If you are referring to financial opportunities, then I think you are asking the wrong question. Business / marketing / people skills are far more important than programming languages for making good pay days. You need to learn to sell!
In the big picture, picking PHP or Ruby is fine unless you have a specific need for one over the other (available libraries?) Since you already know PHP, it would be more important to be highly proficient in PHP before you worry about moving to a different web scripting language. After that, make sure that you are can easily make "boss level" in Javascript and then start working on your mobile skills.
Can't go wrong with JS and mobile!
The next step is to get a lot better at PHP, just learning the language won't be enough you need to become a PHP assassin. Then add JavaScript to your strengths next, strong front end developers are tough to find, get in that space.
And finally, the one thing I urge ALL developers to do, get into mobile! Be sure to take on Java for Android or Objective-C for iOS! If you dominate those, you will be very well off without ever having to worry about the business side of things.