Flight Phuket International Airport departs from Phuket Phuket International Airport at 08:30 and arrives at Singapore Changi Airport at 11:30.
The flighttime is about 2h 00m. The distance travelled ("as the bird flies"): 646 Km. So the average speed is roughly 323 Km.
There is an 1 hour time difference between Phuket and Singapore