rom were are you?
I will be travelling on Indian passport.
It's only 1.5 hr flight from KL to Phuket. So if it's your wish to get there, why not? The travel time isn't so simple though. From KL proper to the airport is about an hour. Immigration and customs requires maybe two. So from your hotel in KL to your hotel in Phuket, it could take 5.5 hrs, maybe 6 depending on immigration to Phuket.
We do not know the visa requirement ,you need to ask your embassy
For 5 day trip, it is not worth it to visit Phuket for 2 days. Better to use your time to explore more of KL.
A flight to Phuket will take to you a lot of time. This time can be better use to explore other parts of KL. Phuket is a beach destination, for you to relax, take day trip out to the islands, explore the caves..etc. You will need at least 3-4 full days to fully enjoy Phuket.