The phrase "hole up" refers to the act of secluding oneself in a safe or comfortable place. There are several synonyms for this phrase that one can use to convey the same meaning. For instance, the phrase "retreat into" can be used, implying that one is withdrawing from certain situations or people. The phrase "lay low" has a similar connotation to "hole up" but with a more low-key approach. "Conceal oneself" suggests hiding or not being found by others, while "take refuge" implies seeking safety and shelter. Other synonyms include "barricade oneself", "sequester oneself" and "isolate" oneself. All these synonyms give one a choice to better explain the act without being limited to one phrase.