It's the original name of the sea. The Philippines referred to a large portion of it as the West Philippine Sea because of EEZ rights. There are five claimants to the WPS:
Taiwan and China (almost all of it)
Malaysia
Vietnam
Brunei
The country with the most installations in the sea is Vietnam.
The Philippines sued China through private arbitration. China did not participate. Arbitration ruled that no country has any claims because no territories are involved, and that countries must negotiate with each other over its use. The ruling ironically goes against arbitration.
Taiwan was not part of arbitration but was mentioned in the ruling. It publicly declared that it also rejects the ruling.
The other three state that they want to negotiate with the Philippines but don't want to give up their claims. Many more countries, including the U.S., declared that they support the ruling but don't want to be involved.
The Philippines has been asking the U.S. for help since the 1990s but the U.S. has not. Later, Pompeo stated that the reason why they can't help is because no territories are involved, and even if conflict breaks out, help is not automatic because given the War Powers Act Congress has to deliberate and vote first to see if the U.S. will help.
Some have pointed out that the reason why these countries were setting up installations in the sea is because they consider the U.S. as a threat. That is, it may through economic sanctions close off the Taiwan strait and control the sea, and it was seen as increasingly aggressive because of Obama's pivot to Asia (after Bush's adventurism in the Middle East). Without a blue water Navy, what they did was to set up what are essentially unsinkable ships in the area.
The Philippines has the weakest military in the region because it was not supported readily by the U.S. It was given overpriced military surplus as aid in exchange for using the bases, and even today it can at best receive only decades-old ships.
However, the country is probably the most fanatic U.S. ally in the region. Multiple surveys across the decades show that the U.S. and U.S. Presidents from both parties have very high ratings in the Philippines, and in several cases higher ratings than in the U.S. itself. It's a weird situation because in the early 1900s, the U.S. committed mass murder in the islands when it took over from Spain.
The problem is that that fanaticism has been tempered by the rise of Duterte, the so-called "Trump of Asia" (although he probably claims, given his 80+ approval rating, that it's Trump who's the "Duterte of North America"), who followed a nationalist stance similar to that of Asian neighbors. He was followed by Marcos, Jr., whose father was backed by the U.S., which in turn backed the father's opponents, to maintain U.S. bases, and who's following a similar although more diplomatic stance.
Meanwhile, the top trading partner of the Philippines is China, where approval ratings are only 15 pct. Its main donor is Japan, which also committed mass murder in the country during WW2. And its main investors include Singapore (which has military exercises with China but buys armaments from the U.S.) and, believe it or not, the Netherlands. One of its arms sellers is now India. Sweden wants to sell it jets, France subs, and Israel small arms and armored vehicles. That's also the same France that's now criticizing the U.S. for muscling in on its submarine sales to Australia.
About Japan, what's also weird is that the main supporter of the Philippines is probably not even the U.S. but Japan, which has been the nicest to it. It also helped that Abe was very friendly to Duterte and vice versa. And yet Japan is generally disliked by China, Taiwan, and South Korea because of what happened during WW2.
It's also the same Japan that appears to be pushed by the U.S. to encourage the Philippines to join Australia to form a united force against China, the same Australia that was mentioned above and has China as a major trading partner.
It's similar to Vietnam, where two million were killed during the war. And yet U.S. approval ratings in the country are high even though the top trading partner (and bully) of Vietnam is China, and its military ally is Russia. And the country that's been pushing to sell arms to it is the U.S.
Finally, it's similar to Taiwan, which has both China and the U.S. has major trading partners but is recognized as neither as a sovereign state. Also, before it became pro-neoliberal, it had almost four decades of martial law administered by a nationalist but pro-business (meaning, it engaged in deals with China to avoid conflict) dictatorship. Also reminds me of Japan, which has been controlled by a Liberal Democratic Party for more than five decades and is not exactly liberal or democratic.
Anyway, if anyone is confused after reading this and sense that I'm rambling, the only thing I can say is the confusion is caused by the incredible levels of complexity and contradictions in that region.