slope, hill
坿 centers on a sloped landform: a hill or incline. The two given meanings are essentially the same idea at different scales.
坿 combines 土 (earth, soil) with 付, which likely contributes the sound. The character expresses a slope or hill made of earth.
The left side is earth 土, and the right side 付 looks like a person attaching to something. Picture earth piled up and attached to a rising slope: 坿 is a hill.
For フ, imagine a hill so steep you say 'foo!' as you climb it: foo -> フ, and the earth slope makes you puff.
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