In most cases you do need an exit ticket when arriving in the Philippines some people do avoid buying one but its not always guaranteed that immigration at the airport won’t check. With continued modernisation of facilities it will soon get to the point where they know if you have a return ticket or not via the computer system. For example when I leave the UK the British tax office know when I leave and arrive via the computer system at the Airports in future I have no doubt this sort of method will be used by more and more countries. You also have the issue that you may get stopped in your home country before you get as far as the Philippines as the airport could be fined for you not having a ticket. What I did find though is initially they would check to see if I had a ticket but after my passport received multiple entries nobody seemed to bother me and its no doubt to do with the fact they would expect me to know what I was doing.
If entering on a tourist visa you will need an exit ticket but for other visa types I recommend checking with the Philippines Embassy in your home country. The reason I say in your home country is the fact the service is more likely to be efficient due to being used to Westernised at the same time saving you money on telephone calls if you need to call.