The Philippines is the only Christian country in Asia, they are also heavily economically linked to America.
It's pretty easy for the Americans to use leverage against them to set up a base if they wanted. Oh, you don't want us to have a military base in your country? Well how about we shut down visas for your citizens. And it would be a shame if the Islamists in your country received funding and weapons.
I have a nagging suspicion (conspiracy theory) that CCP/NPA, ISIS groups that wreck havoc in the Philippines not too long ago are partly funded or is funded by America deep state to ensure that Philippine dependency from American so-called military leadership will always be there. The rebel/separatist movement in that country has never seemed to wane despite the many efforts and eradication drive from the preceding governments.