Many airlines will require you to show one before you are even issued your boarding pass. I have been asked to show an outbound ticket (or resident visa) roughly 75% of the time. Buy an outbound ticket and save the hassle of quickly buying one on your phone at the airline counter. Hong Kong, Kuala Lumpur, Singapore, Taiwan, Bangkok are usually very cheap flights from Manila or Clark ($40-$100 USD). You are setting yourself up for a headache if you don't. And don't be one of those guys that yells at airline staff and causes a scene for your own lack of preparedness/ignorance, knowing and following the rules is 100% on you, they don't make the rules.