bladder
脬 centers on the bladder, a bodily organ that holds fluid.
脬 combines the flesh radical ⺼ with 孚, which likely contributes the sound. The exact historical development of the character is uncertain.
The flesh radical ⺼ suggests a body part, and 孚 looks like a hand over a child, but here think of a fleshy pouch holding liquid: the bladder.
For ホウ, imagine a bladder swelling like a balloon: the 'ho' sound of a deep breath and the 'u' of a full balloon combine to cue ホウ.