PH started out with very belligerent attitudes because of US support. In fact, it is the PH which used fully armed soldiers and warships to harrass unarmed fishermen of China, Taiwan, and other neighbouring countries.
PH not only has conflicts over the Spratly's with PRC China, but also Taiwan, Malaysia and Vietnam.
PH also wants to to Sabath, Malaysia which angered many Malaysians.
PH is aggressive, but no other country wants to team up with PH to go against China, except USA and Japan. But USA will not give up its benefits of collaborating and trading with PRC China.
(Othe countries in ASEAN know too well that PH and Japan are nasty countries. They choose to stay away.)
The only choice PH has is Japan which shares similar values and approaches in dealing with other countries.
PH wants to own the whole area of Spratlys. For instance, the islands managed by Taiwan are far away from PH coast, but PH always makes threats against Taiwan. PH threatens Taiwan that it will take the islands by military forces.
PH has its border line at 118 degrees east longitude. This has been recorded by the international treaties between PH, Spain, USA and Great Britain. In the 1960's PH's constitution enacted by the parliament still enforced this line.
Scarborough Shoal was on the west side of the 118 degree line. That means PH explicitly said the shoal is not PH territories until 1970's (for a 100 years at least). But nothing has been done to the law until 2009. Mr. Victor Archer II pointed this out, but he was constantly harrassed and threatened by Filipinos. The articles was deleted from newspaper website recently.(Mr. Archer II said in his article: "Who are we fooling?")
Therefore, PH has no legal basis for joining the conflict suddenly. China and Taiwan has been consistent in the land claims which is documented and published in many govt documents.
As Mr. Archer II has pointed out PH has made modifications to UNCLOS as a condition for signing the UNCLOS. The aim is to prevent other countries to UNCLOS for land claims against PH. Now PH always resort to using UNCLOS against other countries. PH has deliberately misinterpreted UNCLOS to gain benefits.
PH, be honest. You cannot just have everything your own ways.
You use the law as a trick to gain more benefits but you do not even respect your own law. What an irony!!!