The same will be pretty much true of all the phở cuốn places on Ngũ Xã island, but this was my spot when I lived in the neighborhood, so it’s where I know the menu the best and where I’ve eaten multiple times post-celiac diagnosis.
I’m fairly certain that, with the exception of the Bia Trúc Bạch, the whole menu is gluten free. There may be some mỳ noodles or something with Maggi in it hiding somewhere on the menu, but I think you can be pretty confident that everything is fine. I know for a fact (through conversations in Vietnamese with the staff and eating everything many times that the phở cuốn, phở chiên phồng, and đậu phụ cà chua are all completely fine and that there’s no gluten in the fryer. The staff don’t really speak English, but you really don’t need to talk to them, since there isn’t really anything that could cross-contaminate. Delivery (with no special instructions) is also completely fine.
As a general note for tourists/new arrivals, the vast majority of the food in Hanoi is going to be completely safe. Most of the best local places have fairly limited menus (so no cross contamination) and with VERY few exceptions, northern Vietnamese food is completely gluten free. Obviously bánh mì is off the table, and you’ll want to make sure to avoid mỳ/mì noodles (which are wheat, yellow, and easy to spot). I avoid duck, since it’s often served with soy sauce and you’ll want to make sure that you say no if you’re offered quẩy (a sort of savory donut stick you put in your phở). If you do that, it’s extremely unlikely that you’re going to encounter gluten (and yes, things like bún chả that have meatball-like components will be fine). Vietnam is one of the best places in the world for celiacs and general food safety is extremely good, so don’t miss out on the amazing food here. Happy eating!