Most of the time the enforcement is actually conducted by the airline itself, rather than the Philippine government. The reason for this is because in the end, the airline is responsible if they allow you to fly to the Philippines and you do not have some type of ongoing ticket to leave the Philippines within 59 days.
So, for example, if you travel to the Philippines on Singapore Airlines and you have no ongoing ticket, the government in the Philippines can force Singapore Airlines to return you to your origin at their expense (although, believe me, the airline will come after you to pay the bill!).
Airlines don’t want to get caught up in this sort of situation, so most of the time when you are traveling to the Philippines, the airline will ask to see your ongoing ticket before they allow you to board the plane that will take you to the Philippines. Of course, if you have a round trip ticket, or another ticket to a different destination on the same airline, they already know that you have that ticket, so generally they will not ask for it.
If you have a ticket on Singapore Airlines to take you from Los Angeles to Manila, and a separate throw away ticket from Clark to Bangkok on Tiger Airways, then Singapore Airlines has no way to know, and they will ask to see the Tiger Airways ticket. If you do not have any ongoing ticket, it is likely that Singapore Airlines (or any airline that you are flying, Singapore Airlines is only being used as an example) will refuse boarding to their plane. Often, they will offer you the opportunity to purchase some kind of ongoing ticket before the departure, which wold then allow you the chance to comply with regulations. However, that last minute purchase of an ongoing ticket will not be a bargain, in fact, it will be a very expensive ticket.
Best bet is to have either a round trip ticket, or some cheap throw away ticket before you leave. If you do this, you will be covered and have no hassles along the way.