There are various synonyms for the phrase "getting fat," which can be used to describe a person who has gained weight over time. A few examples of synonyms include "putting on weight," "gaining extra pounds," "increasing in size," "packing on the pounds," "bulking up," and "expanding waistline." The usage of these synonyms depends mainly on context and the level of formality required. It is essential to recognize that gaining weight does not necessarily mean becoming unhealthy, as it can be a part of a specific fitness or medical regimen. It is essential to maintain a healthy lifestyle, including exercising regularly and eating a balanced diet, to keep the weight within a healthy range.