China isn't afraid of a war with US. What did US gain by sending Pelosi to meet with Chinese separatists when they proved incapable of mounting any response to constant new Chinese military patrols for over a year now?
As long as China's slowdown isn't putting US on track to catch up, they're not gonna be worried in the least.
Now, more than ever, China stands in a position of strength over America, not least due to being able to hold the threat of military intervention in the western front against them.
In the SCS, while China is in no rush to settle disputes by force, they've also had a history of never retreating from any holdings. If Philippines can manage to scrounge up one of their few frigates or gunboats and send it at a PLA outpost, it is likely to end in the PH vessel being sunk or towed away, depending on whether they put up resistance or not.
Since US has a history of not mounting an effective response in Asia, China has little reason to consider them part of the calculus. US has even avoided answering Marcos' call to help them resupply their scrap outpost. There is just no indications America would risk further damage to itself by helping such an obviously weak actor.