This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 勏 is uncertain. It combines 力 (strength) with 咅, but the role of 咅 is unclear.
With no clear meaning, focus on the shape: 咅 looks like a mouth 口 under a standing figure 立, beside 力 (strength). Perhaps it suggests using strength to stand and speak, but this is speculative.
For ホウ, imagine a strong person named Hou standing beside the 力 component, ready to act: Hou -> ホウ.