The Philippines is modernizing its navy and has one of the most contentious maritime claims with China, making Indonesia's involvement all the more important, says Auslin.

"There are deep divisions within ASEAN. The view of the Philippines, for example, over territorial issues is very different from Indonesia," he said. "And the reason Indonesia can play a broker's role is because they don't have any of the territorial disputes with China."

The Philippines is taking its case against China to the U.N. Convention on the Law of the Sea. But Beijing is rejecting Manila's push for international arbitration.