You are comparing a language (PHP) to a framework (Ruby on Rails). You should choose a PHP framework (if you want to start with PHP choose a framework: CakePHP or symfony).
My personal preference is Ruby on Rails. I love the Ruby programming language very much for some of its features.
I don't agree with starting any sort of programing with a framework. I have always been taught to learn how a language works in its most raw form in order to understand it and i believe in that.
Learning how the language syntax works and is structured is more important than learning a framework that you go "i want a blog make me one". Though that is a exaggeration as frameworks can be much more complex it still holds true that it is best to get the fundamentals correct before moving on to the shortcuts.
I see the biggest issue with a framework comes when you want to do something the framework does not supply you will be left with having to learn all over again.
Start with the basics, follow some tutorials on ether and get to grips with the basics like variables, loops, and conditional statements then look at the different frameworks and find out which one works for you. I have not yet got to grips with any frameworks just yet as it has taken me a long time to learn how to make functions and classes and a few built in functions that i wanted to get a good rounded knowledge in. Now that i have these skills i am looking at the frameworks and how these would help me develop my applications so far i see little need for them and to me they just make it seem more complex for now having to read though the documentation of all the classes they provide.
If you are planning on building data driven websites you will most certainly want to take a look at SQL syntax for preforming database quires and how to produce a .htaccess file for securing your website as i have had to spend a few weeks plugging holes with the aid of my friend whom is quite the hacker.
For deciding between Ruby and PHP my personal opinion on the matter just now is that Ruby and its framework Ruby on Rails is rather gimmicky and is no better in the long run as PHP and Zend. From what i have read in articles though there is a lot of praise for Ruby on Rails in a lot of situations developers are better served with PHP as it is more mature and scales better with large applications there is also more work for PHP developers and a much larger collection of tutorials, sample code, and open-source classes for you to learn from.