At PHX, drivers must be in one of three special staging areas (geofenced) and are FIFO like a taxi. This surely affects the number of drivers willing to participate, and could lead to more surges (I have not used Uber to give a personal experience).
https://www.uber.com/drive/phoenix/a...ix-sky-harbor/
Edit: It apparently is true of EWR as well (must be on property to get ride requests)
https://www.uber.com/nyc-drivers/airports/ewr/