Yes, there is an airport in Baguio, but it is currently only used by private planes and for chartered flights. Some of the major Philippine Airlines have indicated that they may start flying to Baguio though.
Commercial flights to and from Manila would be nice, but Baguio’s land transportation options can already get people to pretty much anywhere in Luzon with relative ease.
If commercial flights were to start up, one the best possible routes would be between Baguio and Mactan–Cebu International Airport. This would be the perfect combination. Allowing people to travel to and from a cool mountain environment and one with beautiful tropical beaches. Mactan Island is also conveniently situated across from Cebu City. So, it would combine a quaint smaller city with a big city.
Flights to Baguio from many places around the Philippines would probably be popular. Even flights once or twice a week to and from other popular destinations in the Philippines makes sense.
Loakan Airport area is currently not a popular destination to visit, but the view at the end of the runway is pretty impressive. The ride to and from the center area of Baguio and Loakan is also actually quite nice too. An even nicer ride with absolutely spectacular views along the way, is the road going from Loakan down to the Hot Springs in Itogon.