Well, according to China, those waters are their territory, which means that the presence of foreign military vessels is an invasion.
Practically speaking, I think you could call that area a contested region, so minor skirmishes like this are expected and could escalate to war (like Crimea eventually did).
I think that the Philippines approach has been something like, ‘You can claim those waters if you want, but you can’t possibly keep us from entering them, so we’re just going to ignore you until you start killing our people, and then we’re gonna call in big brother America.’
At the very least, they should raise real estate taxes on empty units. This will penalize people for owning several vacation homes, as well as incentivize landlords to lower rates in order to fill the unit.
Difficult to enforce, but send a few people to jail for real estate tax fraud and the rest will fall in line.