For a beginner, I'd say learn Rails. The other frameworks are nice in their own ways but Rails has the largest community by far. PHP is, as others have mentioned, just a language, and while there are good frameworks for it (CakePHP as you mentioned, CodeIgniter, Zend), the first point applies: Rails is still the hot thing right now.
PHP is probably more mature than Rails for web apps (please don't hurt me, Rubyists) but strictly for speed of setup of new products Rails is probably faster.
My answer would likely be different if you were looking to learn to program as a professional.
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For a beginner, I'd say learn Rails. The other frameworks are nice in their own ways but Rails has the largest community by far. PHP is, as others have mentioned, just a language, and while there are good frameworks for it (CakePHP as you mentioned, CodeIgniter, Zend), the first point applies: Rails is still the hot thing right now.
PHP is probably more mature than Rails for web apps (please don't hurt me, Rubyists) but strictly for speed of setup of new products Rails is probably faster.
My answer would likely be different if you were looking to learn to program as a professional.