The phrase "called by duty" refers to a feeling of obligation or responsibility towards a particular task or mission. Some synonyms for this phrase include "duty-bound", "obligated", "committed", "responsible", and "devoted". "Duty-bound" implies a sense of duty towards a certain action or task that must be performed. "Obligated" suggests a legal or moral requirement to fulfill a certain responsibility. "Committed" is equivalent to being dedicated or devoted to a particular task or goal. "Responsible" refers to an individual's accountability and reliability towards a certain task or role. "Devoted" suggests an ardent commitment towards a particular cause, idea or person. All these synonyms convey a sense of duty and responsibility towards a particular task or mission.