The spelling of the phrase "breast up" corresponds to the pronunciation of the phonetic transcription, /brɛst ʌp/. The word "breast" is pronounced with the short e sound, followed by the phoneme /s/ and the final /t/. "Up" is pronounced with the /ʌ/ vowel sound and the /p/ consonant sound at the end. This phrase is often used in the context of improving posture, encouraging individuals to lift their chest and maintain an upright position.