"On the increase" simply means that something is becoming more common or prevalent over time. There are a lot of synonyms for this phrase that can help to add variety and emphasis to your writing. Some of these synonyms include "growing," "expanding," "escalating," "surging," "rising," "spiking," "augmenting," "amplifying," "intensifying," "proliferating," "multiplying," and "gaining ground." Each of these phrases can be used to describe a trend that is becoming more noticeable or significant, whether it's a social, economic, or environmental phenomenon. By using different synonyms for "on the increase" in your writing, you can convey a sense of urgency, importance, or excitement about the topic at hand.