I a researching Loa so that is all this apples to. Guys ride Lao all the time and you can in fact you can rent bikes there if you want to. Gtriders has a section on Vietnam written by guys who have ridden there, if that is an interest it may be a good place for research.
A while back I read something on one trip to Vietnam, as I recall he did mention one at least one occassion he di feel threten, but he did survive to post his information
Ray
Highway 13 that runs through Laos North to South, from the China border to the Cambodian border, is asphalt all the way. You could take a sport bike on it, so it should be no trouble on your Phantom.
Unfortunately in Laos, there are not many loops to do, unless your an of-road rider. So you basically do R13. Options in the North are a run out to
1. Phonsavan & Xam Neua
2. Oudom Xai Pak Beng, & maybe put your bike on a boat to go out to Houei Xai / Chiang Khong, or back down to Luang Prabang.
3. Phongsali from Oudom Xai & asphalt / "easy" steep winding dirt
Then in the south go out to
1. The Vietnam border from Savannakhet.
2. Attapeu asphalt / dirt, do-able on Phantom (back depending.)
3. Pakxe / Bolavens Plateau / Don Khong island.
From Vientiane do a loop that goes out to Thalat & the Nam Ngum dam, then over to Vang Vieng & back down R13 to Vte.