support
戧 centers on the idea of support, likely in a structural or foundational sense. The given meaning is narrow, and the character is rare, so its full conceptual range is unclear.
戧 combines 倉 (storehouse) and 戈 (halberd/weapon). The historical development is uncertain, but it may have originally expressed support or foundation through the idea of a storehouse reinforced by weapons, or it could be a phono-semantic compound where 倉 contributes the sound.
A storehouse 倉 supported by a halberd 戈: imagine a sturdy building propped up by a weapon, giving it extra support.
For ソウ, picture a storehouse 倉 being supported by a saw (ソウ) – the saw's blade reinforces the structure, and the sound 'saw' cues ソウ.