Philippine immigration requires that you have an onward ticket for travel outside of the Philippines. Most airlines will want to see this before they will let you check in for the flight.

Nothing specifies that the onward flight has to be within the 30 days of your visa (you can now actually extend your visa in country for up to three years). However I have heard of people who have been denied boarding when their onward ticket was beyond 30 days. So potentially you might have a problem.

To be 100% safe I would buy a throw away ticket, a flight to anywhere will do, Cebu Pacific or Air Asia normally have sales every couple of weeks and you should be able to get a ticket for USD 20 or USD30