In the Chinese imperial system, 妃 was a rank below 皇后 (empress). The emperor could have multiple 妃, organized into a strict hierarchy: 贵妃 (noble consort), 淑妃 (virtuous consort), 德妃 (consort of virtue), 贤妃 (worthy consort).
usage
Modern usage: 王妃 means princess consort (wife of a prince), used for foreign royals like 戴安娜王妃 (Princess Diana). 妃子 specifically means imperial concubine.
Left woman radical - pictograph of a kneeling figure with hands folded. Indexes 妃 in the female-relations family with 妈 mother, 姐 elder sister, 妻 wife, 嫂 sister-in-law. 妃 names a high-ranking consort or imperial concubine - by definition a female figure - so the radical carries the core meaning.
Right side 己 supplies the sound - jǐ shifted to fēi through irregular Old-Chinese sound change. Same phonetic in 配 to match (with 酉), 改 to alter (with 攵). 己 contributes no semantic flavour to 'consort'; it is a pure sound peg loaned for its rhyme in the older pronunciation.
