The phrase "called on" refers to a person or group being visited or addressed by someone. Some synonyms for "called on" include "visited," "dropped by," "stopped in," "paid a visit," "showed up at," "came to see," "knocked on the door of," "invited over," "approached," and "attended to." Each of these words and phrases may have slightly different connotations or contexts of use. For example, "visited" may be a more formal way of saying "called on," while "stopped in" implies a more casual, unplanned visit. Choosing the right synonym for "called on" depends on the situation and the tone or style of communication.