The phrase "is back" can be replaced with a plethora of synonyms depending on the context. For instance, if someone returns or comes back to a place, you can use phrases such as "has returned," "has come back," "is back again," "is here again," or "is back in town." If something is reinstated or reestablished, you can use phrases such as "is restored," "is back in place," "is resurrected," or "is reinstated." Additionally, if someone or something is recovering, you can use phrases such as "is on the mend," "is recuperating," "is healing," or "is bouncing back." In brief, there are various synonyms you can use to convey the meaning of "is back" accurately.