With a minibus via Krabi this stretch in south Thailand is an easy drive. Big and small coaches are leaving for Phuket almost every half hour. These are either big buses or vans. The best are the medium sized which start in Hat Yai opposite the Tesco Lotus mall and arrive at Phuket at the terminal 2 starting at both ends from 6 am until 9 pm.
Price is about Baht 400,- one way and travel time is up to 10 hours. The worst are the very big buses because they stop continuously. The best are the medium sized units since they only take about 7 hour and won’t stop often. Southwards bound is good organized because they didn't do it the usual chaotic way which means the made one terminal where buses leave and arrive.
The picture of the Phuket bus terminal for the Krabi Hat Yai and Bangkok bus is below from here also coaches for Satun, Ranong, Khao Lak even Pattaya and Koh Samui plus Chiang Mai is served.
Similar coaches travel from Krabi to Bangkok
Hat Yai
is the hub for southern Thailand travel including Phuket and there are several bus terminals for long distance and for local. But as usual there is chaos means main traffic from Hat Yai to the north such as to Krabi, Phuket, and Bangkok can leave from various stations and small travel agents who have a minibus or van parked in front of the office.
The main bus terminal in Hat Yai also has vans available which are faster but they never are on time and on top of it they always circle in the city until they are crammed packed which easily can take more than an hour which finally means they win on the highway they lose in the city which is an irrational behavior.