The phrase "in action" implies that something is happening or being performed. There are various synonyms that can be used to replace this phrase, such as "performing", "executing", "operating", "working", "functioning", "engaged", and "active". These synonyms convey different nuances and contexts of the phrase, but all suggest that something is in motion or happening in real time. For example, "performing" suggests a deliberate and planned action, whereas "active" can imply a continuous and ongoing state of motion. Choosing the right synonym can enhance the tone and precision of one's language, making communication more effective.