怖 rarely appears alone in modern Chinese. It is most commonly seen in compound words: 恐怖 (terror/horror), 可怖 (terrifying), 怖惧 (fear and dread). As a standalone character it is literary.
Heart radical on the left - left-side compressed form of 心 - marks emotional verbs and adjectives. Fear is felt in the heart. Same radical drives 怕 (afraid), 慌 (panicked), 惊 (startled), 悲 (sad), 情 (feeling) and most other emotion characters.
布 supplies the sound directly - bù with the same tone - making this an unusually clean phono-semantic pair. Memory hook: terror 怖 spreads 布 through the heart 忄 like cloth unfolding.
