FWIW, Pho' origin is from the North of VN, so the best place to have Pho in Vietnam is Hanoi. The taste will vary slightly or even vastly for various provinces, but Hanoi is the most "authentic".
Btw, most Pho restaurants in the State are owned by people from the South and don't taste that good IMO. The best Pho I've had is Pho Quang Trung in Garden Grove. The portion is huge for the price and they make pho in northern style. Tip : Hanoi style don't have Pho with bean sprouts and salad.