Antonyms for the phrase "filled a position" could include several phrases based on the context. In a recruitment context, the antonyms could be "vacant position," "unfilled role," or "open job." In a management context, antonyms may be "lack of employees," "understaffed," or "short-staffed." Employers might also describe a position as "unoccupied," "empty," or "unengaged" if they are not looking for someone to fill the position. Sometimes, a particular job is created or opened up, so employers may describe the position as "newly created," "fresh," or "open opportunity." The most suitable antonym would depend on the context and the reason why the position is not filled.