Are there nonstop flights from Sanya (SYX) to Phnom Penh (KTI)?

Yes. Cambodia Airways fly this route. Flight time is about 1h 34m.

What is the fastest connection from Sanya (SYX) to Phnom Penh (KTI)?

via Vientiane ≈ 2h 46m, via Bangkok ≈ 2h 52m, via Nanning ≈ 3h 7m (estimated flying time, excluding layovers).

from 18,000 ANA miles (economy, one way, based on the published award charts).

Sanya Phoenix International Airport (SYX) to Techo International Airport (KTI)・910 km

Nonstop flights available (1 airline). Flight time about 1h 34m. Nonstop return flights also operate.

With milesANA 18,000 miles+ (via SZX)Economy, one way, estimate. Tap a connection for miles by cabin.

6 one-stop options, sorted by estimated flying time. Tap one to see the airlines on each leg and booking links.

Times are estimated from distance. Check schedules, frequency and availability with the airline or a booking site.