How do airports in hot climates handle extremely high temperatures?
Transport aircraft are certificated to a maximum operating temperature for departure that is related to International Standard Atmosphere (ISA), typically 35 deg C above ISA (there may be airplanes certified to ISA +40), ISA being 15C at sea level and dropping from there at the standard adiabatic lapse rate .

ISA temperature at Phoenix airport at 1135 ft ASL is about 13 deg C, so the max temperature you can operate at is 48C, if your plane is certified to ISA +35 (if your plane was certified to ISA +40, you'd be good to 53C).  This is based on the airport temperature reported on ATIS, not temperature measured at the aircraft.  

At 48.9 C in the case you mentioned, you are above your maximum certified temperature for takeoff, so you are stuck until it cools off, and you'll simply have to wait for the temperature to drop a degree later in the day.  This applies anywhere in the world based on the ISA temperature for the airport. So for example at a Middle Eastern airport at sea level, where ISA is 15C, you'd be good up to 50 deg C, and if it's above that temperature, you wait for it to cool off.