all I am saying you need to fly nonstop into the airport in Phuket if you are doing the sandbox,,,you cannot make a connection in BKK to get to Phuket. so you need to find a flight from europe nonstop to Phuket, or any other country but it must be nonstop to Phuket.
meaning you need to fly from a foreign country, you cannot make the connection in BKK, either fly via Europe and straight into phuket or the other direction via an asian country, for example via Singapore..
requirement is still to overnight in BKK for 1 night,,theire should be an option to rebook your continuation flight a day or 2 later to Phuket in that airlines home site...normallt airlines will give you an option to rebook if they cancelled the flight in advance.or request a refund, and then rebook another option that works for you.