The Vietnamese spelling of pho, using an O with horn and hook above, is phở.
The letter “ở” combines an o with a horn diacritic and a hook above it. Vietnamese uses both vowel markings and tone marks, so the spelling records pronunciation more precisely than the unaccented English form “pho.” The hook above marks the hỏi tone in this word.
In English, “pho” is the standard spelling because English-language typography often drops Vietnamese diacritics. That omission is convenient, but it hides information: phở is not interchangeable in writing with forms such as phơ, phò, or phó, which use different markings or tones.
The dish’s name appears in Vietnamese culinary history in the early 20th century. It is a noodle soup made with broth, rice noodles, herbs, and meat, especially beef or chicken. Vietnamese spelling therefore distinguishes the dish’s name from several other possible readings of similar letters.