On the job is often used to refer to working, but there are several synonyms that can be used interchangeably in different contexts. In some cases, one might say that they are "at work" or "in the workplace" to describe their current employment status. Other alternatives include "on duty" or "engaged in employment" to highlight the active nature of the work being done. Other synonyms can include "in the field", "on-site" or "on assignment", which give a sense of being out and about and undertaking specific tasks, rather than simply working in an office or other fixed location. Ultimately, the choice of synonym will depend on the context and the specific connotations of each phrase.