I changed the timezone setting to America/Phoenix, and the result is one hour behind the actual time here in Phoenix.
Phoenix is UTC-7 for the entire year--unlike every other state in the United States, Arizona does not recognize daylight savings time. So, Arizona is in one US time zone for half of the year, and a different time zone for the other half of the year. It seems likely that this detail has been overlooked. Has anyone else noticed this?