Area code 623 serves the western portion of the Phoenix metropolitan area in Arizona, often referred to as the West Valley (including cities such as Glendale, Peoria, Surprise, Avondale, and Sun City). It was created on March 1, 1999, as part of a split of Phoenix’s original 602 area code, with 623 assigned to accommodate the booming suburbs on the west side of Phoenix. The introduction of 623 (alongside area code 480 for the East Valley) was driven by rapid population growth and telecom demand in the 1990s. For over two decades, 623 exclusively identified the West Valley region, where Glendale’s sports stadiums and rapidly expanding communities embraced the new code. By 2023, however, an overlay plan removed the geographic boundaries between 602, 480, and 623, unifying them across the entire Phoenix metro. As a result, area code 623 now overlays with 602 and 480 – ten-digit dialing is mandatory, but callers anywhere in Phoenix can receive a 623 number. This overlay preserves Phoenix’s number supply without introducing a new code, while 623 continues to be strongly associated with the West Valley’s identity and growth.