阜is a picture of a mountain outside of the city, however it is on its side, sideways, rotated 90 degrees fu4
邑yi4 is the city 口 gate; people desire 巴 to enter the city
BOTH use 阝 as the transformed version.
阝on the left: the mountains and hills just outside the city.
阝 on the right: the city gates.
though kou is usually mouth口 seen head on, part of the face; 口 is also sometimes used to depict a city or even kingdom viewed from above, the idea of a walled enclosed protected space.