Phosphorus (element), water rushing between rocks
磷 centers on the element phosphorus, a substance found in certain rocks. The older meaning of water rushing between rocks is a separate, now rare sense that describes a natural scene rather than a chemical element.
磷 combines 石 (stone) with 粦, which likely contributes the sound. The character originally referred to water flowing among rocks, but in modern usage it primarily denotes the element phosphorus, which was isolated from mineral sources.
The left side is a stone 石, and the right side 粦 looks like a complex arrangement of grains or sparks. Picture phosphorus glowing faintly within a rocky mineral, like a hidden light inside stone.
For リン, imagine a ring of phosphorus glowing on a stone: ring -> リン, and the stone 石 holds the glowing ring.