The Department of Foreign Affairs said the US, a long time ally of the Philippines, is interested in ensuring freedom of navigation in the disputed waters.
"It is important for the international community to safeguard freedom of navigation and overflight in the South China Sea. This is of paramount concern to all countries," the department said.
"If the US decides to send naval vessels within 12 nautical miles of the reclaimed low-tide elevation features in affirmation of this objective, this would be consistent with international law and a rules-based order for the region."
A US official said last week that navy ships would sail inside the 12-nautical mile zones that China claims as territory around islands it has constructed in the Spratly chain in the next two weeks.
The Philippines has filed an arbitration case against China at the United Nations tribunal in The Hague, to contest Beijing's claim to nearly the entire South China Sea, and has protested expansion activities on the disputed islands and reefs.
Vietnam, Malaysia, Brunei and Taiwain also have claims of sovereignty in the sea.