The Phoenix line
Central and Midtown Phoenix, Arcadia and Biltmore, Sunnyslope and the north-central corridor, the Bell Road side of north Phoenix, Desert Ridge with Phoenix's Paradise Valley Village, South Phoenix and Ahwatukee Foothills. Twenty-five postal codes in all, every one of them inside or mostly inside the City of Phoenix.
The East Valley line
Scottsdale from its southern neighborhoods to the desert codes north of the preserve, the Town of Paradise Valley, Fountain Hills, Cave Creek, Carefree and Rio Verde, Fort McDowell, Tempe, Mesa from its downtown to the eastern codes along the Usery foothills, Chandler and Sun Lakes, Gilbert, Queen Creek and San Tan Valley. Forty-eight codes across Maricopa County and the Pinal County side of the southeast Valley.
When an address sits near a line
Use the ZIP code on the property's mail. A house in 85254 with a Scottsdale address goes to the East Valley line even though most of that code is inside Phoenix, and a Phoenix address in 85028 or 85032 goes to the Phoenix line even though the area is called Paradise Valley. The full ZIP list settles any doubt, and the lookup on it gives the number for a single code.
Business properties use the same rule. A shop in a Tempe strip center is an East Valley call; an office tower on Central Avenue is a Phoenix call. A property manager with buildings on both sides of the line keeps both numbers and picks by the address of the unit that is wet, not by where the management office sits.
Two codes on this map need a second look because they carry a town's name without being that town. Mail for most of 85331 says Cave Creek, but less than a third of that code's land is inside the Town of Cave Creek, and a home in 85253 with a Paradise Valley address can sit in Phoenix or Scottsdale. Neither changes the line; both are East Valley codes. They do change which office permits a repair, and the community pages spell that out.