There are some well-known phở trademarks in HCMC, such as Phở Bắc Hải, Phở 2000, Phở 24, Phở Hùng, Phở Nga Sơn, Phở 47 (the last two specialise in chicken phở, while others serve both chicken and beef phở; Phở 2000 even offers seafood and vegetarian options). When in doubt, ask any Vietnamese, who will surely have some dearest phở restaurants to present to you, especially if you're an expat because it is definitely one of the must eats.
Here are some restaurants that phở enthusiasts often cite.
Phở Hùng (Southern style)
+84 28 3838 5089
Phở Phượng (Northern style)
https://m.facebook.com/pages/Phở-Phượng/
+84 28 3910 2422
Phở Hà Nội (Northern style)
+84 9 0918 4479
Phở T & T (Southern style)
Phở Trinh (Southern style)
Nguyen Dang Giai, Thao Dien, D2;
Phở Hòa (Southern style)
+84 28 3829 7943
Phở Hùng (Southern style)
+84 28 3927 1888
Phở Lệ (Southern style)
+84 28 3834 4486
For information on street food go to Street Food at Bui Vien