Synonyms for the phrase "seal off" include "enclose," "isolate," "quarantine," "segregate," "partition," "separate," and "block." These words can be used interchangeably depending on the context in which they are used. For example, "seal off" can be used to refer to the blocking of an access point, while "isolate" can refer to the process of separating somebody or something from others. "Quarantine" refers to the isolation of a person or group of people who are suspected of having been exposed to an infectious disease, while "segregate" refers to the separation of groups based on race, religion, or social background. Ultimately, the choice of synonym used depends on the specific meaning and context of the phrase.