Indians can take a flight to Koh Samui and then a ferry to Koh Pha Ngan, but that is expensive. Another option is to take a flight to Bangkok, then a bus/ferry to Koh Pha Ngan. Flights take off from all the major cities of Mumbai, Delhi, Chennai, Banglore.
Chumphon International airport and Koh Samui International airport, both are connected to Koh Pha Ngan by ferry service. So one can arrive at one of these two airports, preferably Chumphon because it is cheaper. Another option is a flight to Bangkok, then a flight to Koh Samui and then a ferry to Koh Pha Ngan.
Buses are cheap but the least comfortable way to travel to Koh Pha Ngan. There are bus services from Bangkok to Koh Pha Ngan.
Speed boats and ferry services from Koh Tao and Koh Samui are available.