dust, earth, bank of earth, to dig, to bring together
坌 centers on earth and dust, with related actions of digging into earth or piling it up into a bank. The sense of bringing together likely extends from gathering earth or dust into one place.
坌 combines 分 (divide/separate) with 土 (earth), but the historical origin is uncertain. It may have originally depicted earth being divided or piled up, but this is speculative.
The top 分 suggests dividing or scattering, and the bottom 土 is earth. Picture earth being dug up and scattered as dust, or piled together into a bank.
For ホン, imagine a huge mound of earth that is the home of dust: home -> ホン, and all the dust gathers there.