The phrase "is back of" can be interchanged with a variety of synonyms depending on the context in which it is used. Some alternatives include "lies behind," "is situated at the rear of," "is positioned on the opposite side of," and "is located in the rear of." Another way to express the same idea is to use the phrase "is in the background of," which implies that the object or idea in question is not the main focus of attention but still plays an important role. Whether writing an essay or simply trying to describe a physical location or position, having a variety of synonyms for "is back of" can help to keep your language clear and varied.