bamboo basket
笊 centers on a woven bamboo basket, typically used for draining or serving food.
笊 combines the bamboo radical 竹 with 爪 (claw), which likely contributes a phonetic element. The exact historical development is uncertain.
The top 竹 suggests bamboo, and the bottom 爪 looks like a claw or a hand. Imagine a hand weaving bamboo strips into a basket.
For ソウ, picture a bamboo basket being sewn together: sew -> ソウ, as the strips are woven into shape.