Phoenix is the fifth largest city in the United States. It is also one of the major hubs of the west, being in a good location (midway north), having good weather for planes, and having America West headquartered there.
I would think there should be plenty of traffic going through there to Taiwan, similar to the amount going through a hub such as Chicago or NY.
PHX was the 11th-busiest airport in the United States in terms of passenger boardings and 35rd-busiest in the world in 2024. The airport serves as a hub for American Airlines and a base for Frontier Airlines and Southwest Airlines.
Earlier this year Eva Air also announced a direct route to Dallas, supposedly starting next month. At the time I felt like it was a tariff negotiation tactic because that one also does not make sense.
I would think there should be plenty of traffic going through there to Taiwan, similar to the amount going through a hub such as Chicago or NY.