medicinal plantago
芣 refers to a specific medicinal plant, plantago, used in herbal remedies. Its meaning is narrow and botanical, with no clear broader conceptual center.
芣 combines the grass radical 艹 with 不, which likely serves as a phonetic component. The exact historical development is uncertain, but it is a phono-semantic compound for a plant name.
The grass radical 艹 sits above 不, like a plant that refuses to be ignored: this stubborn weed is the medicinal plantago.
For フウ, imagine a strong wind (風, ふう) blowing through the plantago leaves, making them rustle: 風 -> フウ, and the plant sways in the breeze.