I’ve nearly forgotten about this option! I didn’t fly within Cambodia at all cos there are way too many cheaper options as you can see in my list.
There are international airports in Siem Reap and Phnom Penh. There are also domestic airports in Cambodia. There used to be more domestic airports (or airfields) but many of them have been closed. Flying between Phnom Penh and Siem Reap is more expensive than taking an intercity bus of course.
Cambodia has their own airlines and they are quite cheap. I didn’t try them. I flew with other airlines.
Cambodians are getting richer than before and international travel has become more affordable especially for people who work in the cities so, many of the Cambodians like to travel overseas now.