@Patrik ******
you can actually speed up the process a bit by making a profile in the eVisa online system selecting Phnom Penh as the consulate (say you're there already) upload ALL the documents in the correct spots EXCEPT proof of you being in cambodia, then SAVE the application in your profile (you can save up to 10 applications)
So that when you get to cambodia you can take a photo of your visa/entry stamp upload it then apply right then.
That's the fastest way to do it