Ship back is a common phrasal verb used to convey the act of returning an item by mail or courier service. However, there are several synonyms that can be used to describe this action. Some examples include "send back," "return by post," "dispatch again," "forward back," "mail back," and "remit." Each of these synonyms can be used interchangeably, depending on the context and the writer's preference. Ultimately, the purpose of using synonyms is to add variety and richness to one's writing, while also conveying the same meaning as the original phrasal verb.