10-12 minutes by car (public taxi) from the ferry port of Tong Sala (Lomprayah and Seatran ferries from Koh Samui arrive here). 10-12 regular planes fly to Koh Samui from Bangkok daily.

Alternatively, you may atake a train from Bangkok to Suratthani train station with transfer to Raja Ferry with 2-3 arrivals to Koh Phangan daily.

Also you can get to Koh Phangan with a joint ticket (bus+ferry) from Bangkok.