Throw in the towel means to give up or surrender. However, there are many other phrases that can be used to express the same sentiment. One such phrase is "call it quits," which means to decide to stop doing something because it's no longer practical or possible. Another phrase that can be used is "throw in the sponge," which was commonly used in the world of boxing to indicate giving up before the end of the fight. You could also say "throw up your hands," which means to give up in frustration or defeat. These are just a few examples of synonyms for the phrase "throw in the towel," but there are many more that could be used in different contexts.