Right phonetic
乃 - supplies the sound (nǎi drifted to rēng, a heavy historical shift but recognisable in the related
仍). Originally a curved-breast pictograph repurposed for grammatical use. Two strokes, the simplest possible right-hand phonetic. Same phonetic in
仍 (still),
奶 (milk) - note
仍 is etymologically the closest relative to
扔.