Phoenix is the capital and most populous city in the American state of Arizona, with 1,608,139 residents as of 2020. It is the fifth-most populous city in the United States, and one of only two state capitals with a population of more than one million residents, along with Austin. The flag of Phoenix, Arizona, is the official municipal flag of Phoenix, Arizona. Its current design is a maroon field with a white phoenix emblem in the center. The design is the second in the city’s history and has been in place since 1990, replacing a flag that was adopted in 1921. 4K Resolution.