final exclamatory particle
嘐 is a rare kanji that functions as a final exclamatory particle. Its standalone meaning is unclear outside of this grammatical use.
嘐 combines 口 (mouth) with 翏, which likely contributes a phonetic element. The exact historical development is uncertain.
The mouth radical 口 on the left suggests speech, and the right side 翏 looks like feathers or wings. Imagine a final exclamation that flies out of the mouth like a bird taking off.
For ホウ, imagine a final exclamation that sounds like a loud 'HO!' echoing: HO -> ホウ.