Yes — "must" is a Dolch Primer sight word. It follows regular phonics rules, but it's taught for instant, automatic recognition because it appears so often in early reading.
You must wash your hands.
"Must" is fully regular in spelling and sound, but as a common word for rules and instructions, it's taught for instant recognition rather than decoded every time it appears in a sentence.
"Must" is fully decodable, so it also works well as short-u sounding-out practice once recognized by sight.
Word Wizard teaches "must" with Flash Cards, Listen & Pick, Spell It, and Write It — four game modes that turn repetition into play.
See "must" with its picture, syllables, and example sentence — with native audio.
Hear "must" spoken aloud and pick it out from similar-looking words.
Build "must" letter by letter from shuffled tiles.
Word Wizard turns sight word practice into a game — Flash Cards, Listen & Pick, Spell It and Write It, from Pre-K through Grade 5.