There are various synonyms that can be used for the phrase "be a passenger". Some of them include "ride along", "travel as a passenger", "go along for the ride", or simply "ride". Depending on context, other phrases that could be used include "catch a ride", "hitch a ride", "jump in the back seat", or "tag along". These synonyms can be helpful when wanting to add variety to your language or when trying to avoid repetition. Furthermore, using these synonyms can help create a more descriptive narrative or dialogue.