This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
胕 combines the flesh radical ⺼ with 付, which likely contributes a phonetic element. The exact historical development is uncertain.
The flesh radical ⺼ suggests a body part, and 付 can mean 'attach'. Imagine a body part attached to something, but its exact meaning is unclear.
For フ, picture a foot (フット) attached to the body: foot -> フ, tying the flesh radical to the reading.