The phrase "hot it up" means to increase the intensity or excitement of something. There are several synonyms that can be used instead of "hot it up" such as amp up, crank up, escalate, heighten, intensify, or boost. These terms can be used in various contexts such as music, sports, cooking, or even a conversation. For example, "I'm going to amp up my workout routine this week." Or "We need to crank up the volume at this party." In any situation where there is a need for added excitement or intensity, using a synonym for "hot it up" can make your language more varied and exciting.