Wow. I got in touch with Tanghalang Pilipino (TP) and they said that almost all 15 shows have already been bought by show buyers who will be selling the tickets. This means that there's not one single dealer of tickets.
To make reserving your tickets a little easier for you, you can call Lorelei or Paolo at TP:
832-1125 loc. 1620 to 1621
Direct Line 832-3661
Or you can contact Lorelei through 09285518645.