The phrase "ebb and flows" refers to the cyclical nature of something that fluctuates or changes over time. There are several synonyms for this phrase that can be used to convey this same idea. For starters, the phrase "ups and downs" is a common way to describe this phenomenon and is often used in everyday conversation. Other synonyms include "peaks and valleys," "swings and roundabouts," and "fluctuations and variations." Each of these phrases conveys the same idea of something that changes over time, and can be useful in a wide range of contexts from personal relationships to financial markets.