Was PHP working prior? And did you follow the last few steps in that guide regarding updating your Yum config and rebuilding easyapache? This is a common issue with LAMP stacks, and is not related to MySQL or Percona itself; it can just be tricky to get all the little pieces in order for the LAMP stack to be happy.
Look in your php.ini file for the below line and make sure it is not commented out:
Then try restarting Apache or whatever webserver you happen to be using.