What will Biden do when China seizes Taiwan? Then, the Philippines?

That worked very well.

We can provide (sell) them the means to defend themselves. Maybe they can and maybe they can't. But the USA has no formal defense treaty with Taiwan.

As for the Philippines- too bad they have a psychopath for a leader.

"In 2017, Philippine president Rodrigo Duterte warned the U.S. that he would unilaterally abrogate EDCA because he received information that American forces were building permanent arms depots to house arms that might include nuclear tipped weapons, in violation of the agreement and of the Philippine constitution.

In February 2021, presidential spokesman Harry Roque said that Duterte had linked the fate of the Philippines–United States Visiting Forces Agreement to "behavior" of Americans toward Fiipinos and said regarding the EDCA, "I think the president wants this to stop... He needs to think about whether to drop EDCA also because that is the legal basis that allows American soldiers and equipment to remain in our country".

...same as every other day.