The Filipino answer would be that if you want me to make your enemies my enemies, give me an ironclad assurance that youve got my back. Like, for instance, a whole lot of military aid.
The US and the other Asians have been telling Manila to build up vs China for nearly a decade now, but they have helped very little.
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.