담기다 means to be put, so it's already a passive voice. But what means 담겨지다 and 담겨져있다? Where they can be used?
담기다, 담겨지다 => This means "has been put in" and implicitly, additionally "it just happened." For example, "사과가 봉지에 담기다." means "The apple has been put in the plastic bag." (Someone has put the apple in the bag.) and it just happened.
담겨져있다 => This means the status meaning "be (already) (put) in". For example, "사과가 봉지에 담겨져있다." means "The apple is in the plastic bag." (Someone put the apple in the bag in the past, so the apple is in the bag now. When you see the apple contained in the bag, you say "사과가 봉지에 담겨져있다."