For People who are willing to Travel to Phuket under the Sandbox Model, They will be allowed to book their Flights via Bangkok. Nothing has been Published yet regarding this issue because the AOT (Airports of Thailand), are Still Preparing and arranging how the Operation of the Transit will be done.
The AOT (Airports of Thailand) is now preparing a Special Transit area in which Phuket Sandbox Passengers will be able to connect their flights to Phuket. Below are some Photos of How this transit area will look like and the progresses that have been made to prepare this Transit Hall.
There will be Signs clarifying everything inside the Airport, and Airport Staff will be guiding the Passengers to go to the Sandbox Transit Hall to connect their Flights to Phuket international Airport.