There are various ways to replace the phrase "split off" with synonyms depending on the situation and context. When it comes to dividing or separating something into parts, you can use terms like break off, cleave, secede, divide, disunite or bifurcate. Alternatively, if you mean that someone left a group or organization, you can say they branched out, exited, broke away, separated themselves, or withdrew. Other synonyms for this phrase include detach, uncouple, disengage, fragment, segment, segregate, and part ways. It's important to choose the right synonym that suits the intended meaning and use actual language to communicate ideas effectively.