Ya Nui beach is little known as it is between Promthep Cape and Nai Harn beach. Nai Harn is a much larger beach with more resorts and places to eat. It is on the road between Promthep and Nai Harn and if driving easy to go right past it. Up to a few years ago almost nobody but Thais visited the beach but now can sometimes get a little over run during high season. Still a very nice place. During the low season when the tides can make swimming dangerous around Phuket, Ya Nui is protected so the tides are a little safer. After the government new rules about beach encroachment of business on the public beach, the few bars and places to eat had to move across the road which is not that bad. I actual think it was good as the beach is a little narrow. Its only about 50 meter walk from the beach to a massage, bar or place to eat. Word of warning about crossing the road. The road here is at the bottom and curves at the top on both ends, The traffic can be traveling fast and visibility not that good till they reach the bottom. There are a couple of small Bungalows to stay at YaNui Bungalows ( http://www.travelfish.org/accommodation_profile/thailand/southern_thailand/phuket/ya_nui_beach/all/882 ) and Naiya Beach Bungalow ( http://www.tripadvisor.com/Hotel_Review-g1215781-d594708-Reviews-Naiya_Beach_Bungalow-Phuket_Town_Phuket.html ) which both have good reviews.
Here is a map on where Ya Nui
here are a few beach views
View from up high looking down from Wind Turbine Hill
few places to eat 50 meters across from the beach
Beach cottages across from beach
Near by The Windmill Phuket Hotel