Southwest Airlines operates out of Terminal 4 at Phoenix Sky Harbor International Airport (PHX). Terminal 4 is the largest and busiest terminal at PHX, serving a wide range of domestic and international flights. Southwest Airlines is one of the primary airlines operating at this terminal. Passengers flying with Southwest Airlines should check-in, proceed through security, and board their flights from the designated Southwest Airlines gates within Terminal 4. It is always recommended to confirm terminal and gate information with the airline or check the airport's official website or app before your flight, as terminal assignments can occasionally change.