I flew from Luang Prabang to Phonsavanh, the flight was only 20 minutes and left 10 minutes early!  If you plan to take the bus, it apparently takes 5 hours along winding roads through the mountains.

Phonsavanh airport is quite basic; your bags arrive in the back of a truck and left on the floor. Also for some obscure reason, they take your passport and write down your details in a book.

It’s probably better to have a room booked before you arrive, so that there is someone waiting to pick you up.  When I arrived there were no taxis waiting. The airport is quite far from the main road.