The Philippines foreign minister summoned China’s ambassador in a move to counter the drawing of Baselines around the Scarborough Shoal in the South China Sea. China claims this island as Hangman Island while the Philippines claim this is a violation of their own sovereignty and international law. The main dispute over this island is a power thing as it is closer to the Philippines while China is trying to assert itself over the entirety of the South China Sea to secure it before any potential retaking of Chinese Taipei (Taiwan).
This international dispute does call into questions the motives as it is relatively obvious that this would be a good strategic gain for the Chinese in offensively expanding it’s maritime territorial claims. They may have expected the pushback but they may have not expected the full scope of the pushback by the Philippines. The United States supporting the common defense of the Philippines could potentially be called into question if the tiny island is seen as an acceptable loss by the Americans but based on current foreign policy towards China it seems unlikely. China may have been betting on a softer incumbent president when it comes to interactions with the US but with a incoming Trump president these last few power moves need to assert China as a power at the very least in the South China Sea before it comes with very harsh sanctions or a powerful stance from the new American administration.
This situation supports the realist theory approach as if you analyze each of these countries moves based on self interest they make perfect sense. China wants to expand its power and is subscribed to a version of offensive realism where as the US/Philippine approach can be seen as defensive because the US being the hegemon and the Philippines being a US proxy. They are just trying to detain and deter the Chinese ambitions in the South China Sea