plug up, shut up
壅 centers on blocking or sealing an opening: plugging up a hole, stopping a flow, or shutting something in.
壅 combines 土 (earth) with 雍, which likely contributes the sound and the idea of blocking or enclosing. The character suggests using earth to dam or plug something.
Earth 土 piled under a blocking shape 雍: imagine using dirt to plug up a hole and shut it tight.
For ヨウ, picture a yo-yo stuck in a pipe, plugging it up: yo -> ヨウ, and the earth piles around it to seal the blockage.
uvula