This is one of my “usuals”, a Vietnamese restaurant one of Paris’s “chinatowns” (13e).
44 avenue d’Ivry, numero 33, C.C. Oslo
75013 Paris
This address leads to some kind of Asian commercial center, you’ll have to go inside and search for this restaurant in one of the galleries, though the “number 33, C.C. Oslo” indication should help.
The Pho is a must (this particular one is “Soupe Tonkinoise” on the menu, 6.50 euros):
Don’t trust the picture, there’s plenty of good stuff in that soup, it’s just hidden 
Rice noodles, the beef is pretty fresh and part of it is put nearly raw on top of the soup and cooks in the soup. Another good one is “Riz Luc lac” (7.90 euros):
This restaurant is one of my favorites when it comes to Vietnamese food, especially as a late lunch on a Sunday (it’s open all afternoon).