Apparently China Airlines and Starlux are both going to fly that route next year. I have a hard time imagining there's demand for one let alone both.
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.