This is required Philippine immigration law. Cebu Pacific is just stuck in the position of enforcing it before a Philippine Immigration Officer does. They don't set the rules. In my real world experience, Cebu Pacific is inconsistent in it's enforcement, as is Philippine Immigration. Cebu Pacific HAS asked me to produce an onward ticket on a number of occasions but not 100% of the time. Philippine Immigration has NEVER asked me for an onward ticket but I HAVE seen them ask others and make a major ugly issue about it. There also seems to be a racial and nationality component as well since Asian passport holders and persons who appear Asian seem to be targeted much more than white western passport holders even when the rules are the same. Just reporting what I have observed.

A simple paper printout of an e-ticket will suffice. Not that I would recommend anything against the rules.... but they don't check anything against computer if someone who wasn't me ever took 5 minutes editing a printout in Microsoft Word.