There are a number of synonyms for the phrase "catch fire." Some of the most common ones include ignite, blaze, burst into flames, combust, and flare up. Other options include kindle, start burning, burn, flash, and scorch. These phrases can be used in a variety of contexts, from describing a literal fire that has started somewhere, to describing an idea, trend, or movement that suddenly takes off and becomes wildly popular. Whatever the situation, using a different phrase for "catch fire" can add variety and nuance to your writing or speech.