Neither countries are a threat without the US, it makes no sense to go to war with neither unless US uses them to attack China, in which case the war will still be against the US and Japan and Philippines become a distraction that China should aim to spend minimum effort to neutralize. It's the same as Taiwan, defeat the US and the war ends, its US goal to see China fight their colonies rather than itself and it's China's goal to engage US and only the US.
Which is why PLA exercises are about blockades, not landings. China is in the same position as US was in WW2 watching Japan take over South East Asia. Cutting US off from Asian industry is the same as cutting Japan off from oil, it forces US to enegage a much stronger industrial power across the Pacific, whom they're reliant on, directly, rather than allowing the US gather strength slowly through piecemeal takeover of small nations.
The current goverment will likely define clear objectives and wrap it up at the objective, what we can't know is what a future goverment, made up of people who grew up with embassy bombings and spy plane collisions, will still define the objective to be purely regional, or will it become the permement neutralization of western threat. Chinese history is full of swings between defensive and problem solving.
