Capt Kornphoomphot Pongpaiboon of the Thalang Police was notified of the accident, near the Shell petrol station on Thepkrasattri Rd southbound in Tambon Thepkrasattri, at 7:40am.
Officers along with Kusoldharm Foundation rescue workers arrived to find the motorbike, a Phuket-registered black-red Honda PCX, demolished by the side of the road.
Its driver, Thanongsak Raiyai, 24, a resident of Moo 7, Nuea Khlong, Krabi Province, was lying dead nearby. He had broken his neck and died instantly at the scene, police said.
His passenger, Piyaporn Kittikulnatee, 30, was injured in the accident, and was rushed to hospital.
From their initial investigation, police said that Mr Thanongsak had just returned from his home in Krabi when he lost control of the motorbike and struck the sign by the side of the road.
Police are continuing their investigation into the cause of the accident, officers said.
According to the national Thailand Road Safety Committee (ThaiRSC), Phuket suffered one death and 63 people injured in road accidents yesterday (Mar 5).
Already so far this year has recorded 25 people have died and 4,230 people have been injured in road accidents on the island since the start of the year.
Five people have already been recorded as injured in road accidents in Phuket today (Mar 6).