having two passports

[IainBusby]

It's a pity you can't use the Filipino passport to enter the Philippines, so you'll have an unlimited visa and then use the British one to exit, cos if show a Filipino on exit I think you'll still have to pay the Philippines Travel Tax.
Iain.

[A_flyer]

It's a pity you can't use the Filipino passport to enter the Philippines, so you'll have an unlimited visa and then use the British one to exit, cos if show a Filipino on exit I think you'll still have to pay the Philippines Travel Tax.
Iain.

Nope, you may pay only the P200 exemption as having a permanent residency abroad with the British passport.
But as I never saw the case, I don't know if you will even have to pay the P200. The only thing I'm sure is that you will not have to pay the full tax at P1620.

As I said, you must use the same passport when entering/exiting or exiting/entering a country to avoid any difficulty as all entry/exit are recorded by immigration (whatever the country is).