After my original post, I learned through comments and Twitter discussions that I got the Philippines position a little bit wrong and that the legality is even more nuanced. So the Philippines does claim the islands as sovereign territory, but claims them as a “rock.” A “rock” is different than an “island” in the UN Law of the Sea – a distinction I would have not thought of. Islands must have an “economic life of their own” if they have no permanent human population. Unlike an island, rocks get no extension of Economic Exclusion Zones (EEZ). Though Taylor Fravel says that if the rock still peaks over the water during high tide, they can get a 12 mile radius territorial sea.
What makes all of this interesting is that, technically, a court could rule that the “rocks” are Chinese but most the water around it belong to the Philippines. What it really does, though, is significantly weaken China’s case for the South China Sea claims. Even if they were to “belong” to China, their economic rights via the EEZ wouldn’t be nearly as large as they’re claiming because most of the shoals, sandbars, and reefs they claim would just be “rocks.”