Mounting up is a phrase that refers to something increasing in size, number, or intensity. It's often used in situations where there's a gradual buildup of momentum or pressure over time. There are several synonyms for mounting up, such as accumulating, rising, augmenting, expanding, escalating, and growing. These words can be used interchangeably depending on the context of the sentence. For instance, if you're describing the increase in tensions between two groups, you can say that the tensions are mounting up, escalating, or augmenting. Using synonyms for mounting up can make your writing more varied, exciting, and engaging, and help you avoid repetition.