@Kevin ***
Are you talking about old Test&Go or new Test&Go with day 5 quarantine and test?
If old Test & Go you can fly wherever you want after you get out of your day 1 hotel, and bring your pink slip to an approved hospital on day 5 to get tested.
If you are talking about the new Test&Go, you can go to Phuket after you get out of your day 1 hotel, and either go to Phuket for a few days and fly back, or just book your day 5 quarantine and test in Phuket and stay there longer if you want.