Mouth radical on the left, the indexing component. Any character built with 口 on the left side usually involves speaking, calling, or noises from the mouth - see 叫, 喊, 呼, 唱. For 唤 'to call, to summon', the mouth contribution is direct.
Right side 奂 provides the sound exactly - same syllable, same tone. The same phonetic appears in 换 to exchange, 涣 to disperse, and 焕 brilliant. Recognising this family helps lock in the huàn reading.
