It's not 幻妃, it's just 妃, common concubine, can read in historical books about Chinese emperors daily life.

妃 = a high ranking concubine of the emperor or wife/concubine of a prince. The rank depends on the dynasty. In the Ch'ing dynasty, it is the 3rd rank after the empress (皇后), 皇贵妃 (imperial consort, Han Dynasty equivalent 夫人) 贵妃 (noble imperial concubine) 妃(imperial concubine ) 幻 = fantasy, virtual. So most probably a character from some fantasy novel.

I think that might be a person's name in some novel