I know that there is a road from Paktha to Hatsa but was told by a guy who works in Hatsa that there was no road from Hatsa to Phakhop. However, that was a year ago and things may have changed by now.
The road from Paktha to Hatsa is do-able by truck but is quite dusty (was there last week). There is also a road from Hatsa to the east to Pha Oudom and onwards to Pak Beng. Don't know the condition of that road but was told that you could do it with a truck.