The Best Sunsets on Phuket's Beaches:
 

Nai Thon Beach, Nai Yang Beach, Surin Beach & Bang Tao Beach Sunsets

[above right]: Nai Thon Beach Sunset (the light is a fishing boat, not the sun)

The west side of Phuket is where you'll see the great sunsets, often as not while sitting at a restaurant with a wonderful ringside view. 

Surin Beach [below] is home to many beach shack restaurants right on the sand - a great place to go for a great dinner and wonderful sunset.

Above: Surin Beach at sunset

Nai Yang Beach is also home to many beachside restaurants and offers up great sunsets around the point at the south end of the bay.

Above: Nai Yang Sunset

Bang Tao Beach also offers many dining options for the evening, all right on the sand of the beach.

Below: Bang Tao Beach sunset from Lotus Restaurant

Wow!  Where will you be at sunset?

Any beach along the west side of the island will reward you with fantastic sunsets.  South of Kata Beach along the coastal road to Nai Harn sits a great - though crude - little bar/restaurant perched on the cliffs overlooking the sea - great location to sit and enjoy the sunset.

Another great place to enjoy the sunset is the Sunset Point Restaurant, just a few kilometers north of Patong Beach.  The dining room sits right over Naka Bay (the next beach north of Kalim and Hin Tang Beaches) - and offers fantastic views of the coast line and sunset.  The food there - unfortunately - is a bit pricey and mediocre - so just have something simple and focus on the beauty of the setting - it is worth paying for.