Even if the Philippine had wanted to get involved , what actually they can bring to the conflict, apart from talking ?
I doubt Japan would get involved directly (unless get attacked), remember Japan has been and will be forever close neighbour to giant China, whether they like it or not, while USA is thousands miles away and Japanese know that sooner or later the US will be eclipsed by China and gone from Asia. Japanese are not stupid, they just polite and not saying it openly
Current Philippine govt and officials are interesting and stupid, do they really think the US is ready to die for them?
Vietnam is a good example for what Japan can do because they seem to get the China dilemma the best. Vietnam is one of the countries that most aggressively opposes China in the South China Sea. And it makes sense if you think about it: Vietnam has fought wars against Japanese, French, and American occupation forces. But what country is Vietnam most afraid of? It's China. And that makes a lot of sense because after Vietnam's other enemies stop fighting,
they leave but China is always right there. As a result, over the last 2000 years, China has occupied Vietnam for centuries and been at war for centuries.
But if China were to ever go to war against Taiwan, what is the likelihood that Vietnam would join the war against China? It's zero. The reason is quie simple: if China wins in such a scenario, they will be able to enact whatever retribution it wants against Vietnam, and there's nothing the latter can do about it, and no country will jump in to intervene. Even if Vietnam would be on the winning side,
they're still screwed. Why? It's because China will still be there, and it will regain its strength eventually. It might take five years, or it might take thirty years, but it will get there. And when it does, it will be sure to make Vietnam's life miserable.
Japan is in pretty much the same situation as Vietnam. China seizing Taiwan will expose Japan's disputed territory but going to war would lead to much more dire consequences regardless of which side wins. This decision is all the easier to make as it becomes ever more clear that not only is it unlikely for the Americans to win in the Western Pacific, but their odds look worse and worse by the year.
The Filipino leadership isn't interested in any conflict with China. The Filipino military is anemic and would offer almost no combat value against China. Instead, they're motivated by two factors. The first is that as long as Philippines is aggresive against China, they get credit from the US and cash it in for monetary and other types of incentives. The other is that the Americans have some sort of leverage over Bongbong Marcos so he has to do their bidding. I don't think that this leverage is strong enough to force Philippines to become a belligerent though.