Philippine Airlines is not part of any alliance.
The only other airline I know that flies to DAVAO internationally is Silk Air, sister airline of Singapore Airlines.
However, they only have 3 or 4 flights a week via Cebu to Davao from Singapore.
You could otherwise just ge a reward ticket to MNL on other carriers that participate in your program and buy a domestic ticket seperately as they are very inexpensive within the Philippines.
Good Luck.