The airport of Skiathos island is only 5 minutes drive to the harbor by taxi, which you do not need to pre-book. The taxi stand is just outside the exit of the terminal building, on the opposite side of the road, from where you may pick up a cab directly to the ferry / hydrofoil ticket office at the port. There is no local bus to do this route.
Skiathos Taxi Federation telephone number: +30 2427024461