Flight Phuket International Airport departs from Phuket Phuket International Airport at 11:40 and arrives at Singapore Changi Airport at 14:55.
The flighttime is about 2h 15m. The distance travelled ("as the bird flies"): 646 Km. So the average speed is roughly 287 Km.
There is an 1 hour time difference between Phuket and Singapore