wild duck, end, suffix
鳬 centers on a wild duck, with extended uses as a suffix or ending marker, likely derived from the duck's tail or final position in a sequence.
鳬 combines 鳥 (bird) with 几, which may have been a phonetic or semantic component. The exact historical development is uncertain, but the character is associated with a wild duck.
The bird radical 鳥 on the left suggests a bird, and the 几 on the right looks like a small table or stand. Imagine a wild duck standing on a low table, marking the end of a line of ducks.
For フ, picture a wild duck making a soft 'fu' sound as it lands on the water: fu -> フ.