Can anybody out there tell me if there is a way to fly from Siem Reap to Phuket without going through Bangkok? I'm thinking of flying into Phnom Penh from Bangkok, taking the bus to Siem Reap, leaving Siem Reap and going to Phuket. Any brilliant ideas? Or is it totally necessary to fly back to Bangkok? Thank you in advance!

From what I can see from the website for the airport authority of Cambodia, see http://www.cambodia-airports.com, there are no direct flights between either Siem Reap and Phuket or Phnom Penh and Phuket. You have to connect through another city. That could be Bangkok, could also be Singapore or Kuala Lumpur; however Bangkok is probably going to offer the most flights to Phuket. But if you are going to be in either Singapore or KL for part of this trip, then routing yourself to include them may work well.

You can fly from Bangkok non-stop to Siem Reap on Bangkok Air, so you may want to do that just to avoid a longer journey by bus.

As Cicerone says, there are no direct flights from Siem Reap to Phuket. There are excellent connections on Bangkok Air through Bangkok.

I assume you are thinking about flying to PP then taking the bus to Siem Reap to avoid the high airfare from Bangkok to Siem Reap. If so, consider the Bangkok Air Discovery Pass which will safe you a significant amount of money on a BKK - REP - BKK - HKT - BKK itinerary. Look at the Bangkok AIr website and read some of the many posts here about the Discovery Pass.

In February 2009 we flew from Siem Reap to Phuket using the Discovery Airpass. I think that technically it would be termed a direct flight (#924, a number still in use), though not a non-stop direct flight--you deplane and reboard in Bangkok. They expedited the clearing of customs and immigration in BKK for through passengers.
One nice feature of the Airpass is that REP to HKT counts as only one leg.

I was curious about the meaning of "direct flight" and looked it up. Here's what I found from an online travel agents dictionary: "Any flight between two places that carries a single flight number. Unlike a nonstop, a direct flight will make one or more stops between the two places. The passenger may have to change planes or even change airlines. This is a change in meaning. In the past, direct flights made stops but required no change of plane."
On reflection, I think that flight 924 did involve a change of planes in BKK because we had to move through the airport from an international arrivals gate to a domestic departures gate, going through customs and immigration en route. It was a short connection, but a Bangkok Airways agent led the way for all passengers involved.