you can buy the alcohol only when allowed to buy.
Only 'from 11:00 to 14:00' & 'from 17:00 to 00:00'
If not the above hours, you can't buy at super-markets, 7-11 or Department stores.
Also, there are some days when no alcohol to sell during the whole day.
Big holidays related with Buddhism, King's birthday, Queen's birthday or Election day.
Not only in marts or stores, but also in restaurants & bars.
But if you stay in Karon pool villa,
you can buy some beers from the small store near the villa.
Please ask to the villa staffs.
You can enjoy the cool Thai beers any time in Phuket.