The phrase "pucker up" is commonly used to describe the action of forming the lips into a tight, pursed position. However, there are various synonyms that can be used depending on the context and situation. Some alternatives to "pucker up" include "pout" which implies a sulky or displeased expression, "pincushion" which describes the puckered lips of someone who is deep in thought, and "kiss" which denotes the action of pressing one's lips against something or someone. Other substitutes for "pucker up" include "tighten" or "compress" which can convey a more serious or tense expression. Ultimately, the choice of synonym depends on the intended tone and meaning of the sentence.