Despite having a Vietnamese-Cantonese-American fusion restaurant (ugh) in Cheyenne, your cravings can only be satisfied at a sushi bar in Laramie and a bakery in Gillette.
Vietnamese restaurants in Nevada, Montana, Nebraska and the Dakotas tend to be clustered near metropolitan areas, so there are others who share your travel struggle. West Virginia also only houses one phở spot, but at least it’s a dedicated Vietnamese restaurant in a relatively small state.
Although the brother and sister behind Mizu come from a Vietnamese restaurant dynasty, their restaurant leans heavily toward Japanese cuisine. According to their Yelp reviews, their phở is massive and delicious, but Mizu is practically on the Colorado border.
Pho and Bakery 59's Facebook description tersely reads, "Vietnamese noodles and French bakery."
I'm not sure Wyoming knows how to fusion.
Depending on your location, it might actually be easier to drive to a different state, for phở's sake.