There are several synonyms for the phrase "on an upper floor", such as "upstairs" or "on the upper level". These terms refer to a higher level of a building and are often used to describe the location of a room or apartment. Other synonyms include "on a higher story", "on the top floor", or "at an elevated level". Each of these terms conveys a similar meaning and can be used interchangeably depending on the context of the sentence. When discussing the location of a building or room, using synonyms for "on an upper floor" can add variety and interest to your writing.