Hi CMFDan,US can and will use Subic and Clark airfields. It's the real reason both Philippines military and Duterte doesn't want to fully utilize the Clark Intentional Airport.
Subic is use for replenishment and supply, while the BASA airbase in Pampanga is where the American build their Arms Depot. Both Subic and Clark are commercial venture, will never be reverted to military bases again cause the govt invested a lot of money to make it commercially viable. Both will serve as a new growth center in Central luzon to jump start that region economy and to decongest Metro Manila. Now if you had gone to Clark its land price had risen significantly, the govt had relocate a lot of its govt office and function there. It will become a new BGC or MAKATI.
Regarding Clark International airport, you are wrong, the govt had just finish the construction of a new airport terminal, a second runway is under construction. The problem with Clark airport is just to far away from the capital Manila, it will take an approximate 2 to 3hours travel time to reach the airport, the new rail line will solve that problem but had to wait 4 years to complete. Now a new super airport will rise in Bulacan under a private venture headed by SMC under MR Ramon Ang, this airport will have 6 runway and able to handle about 80 to 100 million pax annually. Here you can see the POLITICAL WILL of president Duterte, He ordered it approve against the wishes of his Financial adviser who see this projected as detrimental to Clark airport project and are the one delaying the approval. The private venture will not cost a single peso from the govt and is nearer from the capital.