Pho has origin from North, There are 2 places which are famous for Pho, those: Nam Dinh & Hanoi. So truly you will find best Pho in Hanoi.
49 Bat Dan is one of best places for Pho Bo (beef). Otherwise Pho Cham at 63 Yen Ninh is famous for Pho Ga (chicken)
Cheers!