gong stick, drum stick, type of tree
枹 centers on a wooden stick used to strike a gong or drum, and by extension can refer to a type of tree, likely one whose wood is suited for making such sticks.
枹 combines 木 (tree/wood) with 包, which likely contributes the sound. The character originally referred to a wooden drumstick or gong stick, and later also came to denote a type of tree.
A wooden (木) stick wrapped (包) in cloth at one end to strike a drum or gong. The tree meaning comes from the wood used to make such sticks.
For フ, imagine a drumstick flying through the air with a whoosh sound: whoosh -> フ, as the stick strikes the drum.