阪

Left mound radical — the side-form of 阜, picturing stacked earth/terraces seen from the side. The indexing radical, anchors 阪 in the terrain/elevation family: 阶 step, 险 dangerous (terrain), 阻 obstruct, 陡 steep, 隅 corner. Marks 阪 as a feature of sloped land — a hillside or slope, the original meaning preserved in the city name 大阪 Ōsaka (literally 'big slope').

Right 反 supplies the sound — fǎn shifting to bǎn with consonant change. Pure phonetic role; the 'reverse' meaning contributes nothing. Same phonetic family: 板 board, 版 edition, 饭 cooked rice, 返 return, 贩 trader. The slope is one of the simpler 阝-mound chars and a useful reading anchor for Japanese place names ending in -saka.