In many situations it is always easier for the U.S. Citizen to come to the Philippines to meet the prospective foreign fiancee?
All you need is a U.S. Passport for starters and can stay in he Philippines for up to 30 days without any visa.
During your trip please save all receipts such as trip itinerary, boarding pass stubs, hotel receipts, restaurant receipts, gift receipts etc..
The couple will want to have their picture taken together in many settings and look like a happy couple so that the relationship appears genuine and sincere? Other documents can be delivered to the alien fiancee and also the sponsor can be picking up some from her depending on your case?