This is very much like what happens when a Filipino family has a member find work overseas: The family back in RP expects hefty financial support, even when the overseas worker has a family of their own in their new home to support. (Been there, done that.)
This is not a matter of the US asking RP to make China an enemy. In the absence of the US and RP's other Asian allies, China will eat major chunks of Filipino territory and very valuable resources. RP is the swimmer, China is the hungry shark. Where (and why) would the shark stop? Duterte says negotiate? He has NO strength or position to negotiate from, unless it comes from common cause with others. The RP on it's own? Good luck with that.
The Philippines is strategically indefensible. It has an almost purely air-naval problem of defense, against a world power. It is completely dependent on maritime trade not just for its foreign trade but also its entire domestic economy.
Geography is everything.
Vietnam can defy China by daring it to invade overland, and can live off its ricefields until the Chinese get tired of the slaughter as the enemy has to fight through hundreds of miles of earthworks defended by cheap light infantry. But the Philippines has to defend every internal shipping lane, using the highest technology means in large quantities against air, missile and submarine attack, or it starves. Heck, its got such internal bottlenecks that knocking out a series of highway bridges could make Manila uninhabitable.
The Philippines is a third world country with a first world defense problem. It would take an investment of @50billion to begin to credibly address its problem. Its entire government budget though is $50Billion.
So it needs very powerful friends or it needs to bend. That is the problem of geography.