Unlike many American cities that were named after a foreign King or Queen or a conquering soldier invading already inhabited land, Phoenix has a more symbolic name. The local lore tells of a vote being taken on the newly colonized land. The town went through multiple names before someone suggested Phoenix. Several centuries earlier, Grande Pueblo Native Americans had inhabited the land before the dry climate had driven them elsewhere. Since a new settlement was rising from where there had once been another, much as the legendary phoenix does, everyone agreed this name was appropriate.
The brains behind the settlement of Phoenix belonged to Jack Swilling. In 1867 this man was reportedly riding through the desert when he looked down and spotted what was potentially good farm land simply in need of some water. Swilling would later organize the Swilling Irrigation Canal Company, which he moved into the valley. The same year, the company began digging a canal to divert some of the water of the Salt River onto the lands of the Valley.
Phoenix was officially recognized as a city on May 4, 1868, when an election precinct was formed there. In June of that year, the first post office was established with Jack Swilling functioning as the head postmaster.
Phoenix's development since the 1950s has definitely proved to be its strongest. In 1950, Phoenix had an area of 17.1 square miles and a population of 106,000 that placed it 99th among American cities. Today, the city covers about 470 square miles and has a population of 1.15 million, ranking it seventh in the country.
Phoenix's strong growth was by no means a fluke. Its citizens have proven time and again to be very involved in city government. Since 1950, the National Civic League selected Phoenix four times as an "All-America City" in competition with hundreds of other cities and towns across the nation.
Sources:
http://phoenix.gov/CITYGOV/history.html#BORN
http://www.coppersquare.com/
http://www.hellophoenix.com/History.Cfm