For various reasons I'll be the first to voice opposition against any major war with Vietnam just for war's sake. I don't care Phi.
The smartest move China should make IMOO should be to use marine corp to surprise-attack both Phi and Viet-controlled tiny islands/reefs in South China Sea aiming to completely control them within a day or two with minimum death toll for all sides. The timing could be on the eve of Olympics opening ceremony or some int'l festeval a la Goergia-Russo conflict of 2008?
Then Chinese navy can announce the area a millitary exercise zone, and will destroy ANY fresh foreign vessel sent into the area later. IF some supporting warships of Viet and Phil do turn up, destroy them each and all with resolute means once inside Chinese waters. In this way, China can regain SCS with minimum prices since any incoming warships would be considered as invading forces and China will have both obvious legal obligation and moral highhorse to destroy them, needless to say that the dealth toll of such a conflict would become minimum, for all sides - to limit int'l impact.
In front of far more powerful Chinese navy and the complete Chinese control of SCS, Viet and Phil thus dare not and would not send any vessels despite shouting outragously in the press. The US would likely condemn it diplomaticly and that's it, cuz it can not and will not risk or damage far more important Sino-US relations for some tiny sea reefs that belonged to China in the first place. In other words, despite the presence of the US navy in Phil, it will not have direct confrontation against the Chinese navy at all.
The whole operation must be done quick, but very quickly and sharp, best mimic what the US has done to the Panama Canal.