Flight Suvarnabhumi Airport departs from Bangkok Suvarnabhumi Airport at 17:05 and arrives at Phuket Phuket International Airport at 18:30.
The flighttime is about 1h 25m. The distance travelled ("as the bird flies"): 290 Km. So the average speed is roughly 205 Km.
The best day to arrive at Bangkok is Tuesday and it would be best to avoid Monday, as prices are on average 506.82% higher than on Tuesday. (Average prices, based on 21436919 datapoints.)
We have a lot more statistics for flights VN 3989 and between Bangkok and Phuket.