The Name
Does the word pho come from the French pot-au-feu?
Probably not, even though it is the story everybody tells.
The popular version says pho comes from feu, the French word for fire, as in the beef stew pot-au-feu. It is a lovely story. Two problems with it.
First, the sound does not work. The French feu is not pronounced the way pho is. Linguists have pointed this out for decades.
Second, there is a better candidate. Most language scholars favour a Chinese origin: the Cantonese dish ngau yuk fan, written 牛肉粉, which means beef noodles. Vietnamese forms like nhuc pho shorten neatly to pho. A Vietnamese dictionary from around 1930 already defined pho by way of phan, the Vietnamese pronunciation of the Chinese word for flat rice noodle. Scholars including Le Ngoc Tru have supported this reading.
There is also a plausible physical path for it. Chinese vendors were selling beef noodle dishes in Hanoi at exactly the time pho was forming, around 1908 to 1909. Words travel between people standing next to each other.
So where did the French story come from? Most likely Gustave Hue's 1937 dictionary, which linked chao pho to pot-au-feu. Once a dictionary says it, everybody says it.
We are not going to pretend this is fully settled. It is not. But if you want the version the evidence actually supports, it is the Cantonese one.