Ko Pha Ngan is relatively safe even at night for solo female travelers. It is a well-known tourist and backpacker destination, so you'll often find other travelers around. However, like in any location worldwide, it's important to stay vigilant, particularly during the Full Moon Party when alcohol consumption is at its highest. The majority of locals are friendly and helpful, but it is recommended to stay on well-lit streets, avoid deserted areas, and always inform someone about your whereabouts. Reputable taxis are also readily available.