The Phaser 3010 doesn't duplex so it is not a ppd option.
The only way to duplex is to choose (in the Windows driver) manual Duplex, which just prints all the odd page numbers simplex, then you put the output back in the tray and it will print the even numbered pages simplex on the other side of the previous printed sheets. Linux as far as I know doesn't support this, and I know the Xerox ppd doesn't.
I installed driver for my printer from official site, but I can't set duplex(2-sided printing) in Xerox Phaser 3010. When I try to edit property "sides" I haven't any choise, only one-sided printing! I've made setting in cups, but there isn't property "sides" despite of line "Driver:Xerox Phaser 3010 v1.0 (grayscale, 2-sided printing)". So, how can I solve problem with duplex?