I'd say getting started with PHP is certainly easier. Learning a script-oriented languages usually is. If all you're really interested in is writing web-based scripted programs, that's an excellent way to go.
I can't imagine too many people who have taken either of the certifications you've listed would know a lot about the other one.
Make visible what, without you, might perhaps never have been seen. - Robert Bresson
Is learning PHP simpler than learning Java (with no previous programming experience)?
Which exam is more difficult? OCPJP or Zend Certified Engineer für PHP 5.3
Learning enough about any language/technology so that you can actually do something worth while with it takes about the same amount of effort. If you just want do to System.out.println kind of thing, learning how to do it one language might be easier than the other ;)