The United States has a decades-old security alliance with the Philippines that includes a mutual defence treaty and a 2014 pact which allows the US military to store equipment on nine Philippine bases.

With President-elect Trump assuming office on January 20, many in the Philippines are wary about the future of Manila and Washington's relationship.

But Marcos "expressed optimism in maintaining the strong and dynamic relationship" between the two countries -- particularly on economics, defence and security -- during a phone call with outgoing Vice President Kamala Harris.

"The progress that we have made is terribly encouraging and we just hope to build on that," said a statement from Manila's Presidential Communications Office, quoting Marcos during the call.

He also hopes the two countries "continue to stand for our shared values and the rule of international law".

The call with Harris came the same week Marcos held a call with outgoing President Joe Biden and Japanese Prime Minister Shigeru Ishiba where they reaffirmed their commitment to "advance a free and open Indo-Pacific".

The Philippines and Japan -- both longtime US allies -- have stepped up security cooperation with Washington to blunt China's efforts to control most of the disputed South China Sea.

In her call with Marcos, Harris "underscored the strength of the US-Philippines alliance and people-to-people ties and noted it was critical for preserving a free and open Indo-Pacific," a White House statement said.

"The Vice President affirmed the importance of continued defense of international rules and norms in the South China Sea in the face of provocations from the People's Republic of China and noted the United States must stand with the Philippines in the face of such provocations and the enduring nature of the US defense commitments to the Philippines," it added.

Marcos and Harris "also discussed trilateral cooperation with Japan as a key pillar of regional security", the White House said.