The largest city in the Southwest United States is Phoenix.

Phoenix, located in Arizona, is the largest city in the Southwest U.S. It has proliferated in population over the years, becoming the fifth-largest city in the entire United States. Known for its scorching summers and beautiful desert landscapes, Phoenix is the region's major cultural and economic hub. The city offers modern urban development, a vibrant arts scene, and easy access to outdoor activities such as hiking in the nearby desert and mountains. It is also home to numerous tech companies, making it a rising economic powerhouse.