There are several synonyms for the phrase "dumb oxen," which generally refers to a group of people or animals who are considered stupid or lacking in intelligence. One alternative phrase is "brainless beasts," which carries a similar connotation but emphasizes the lack of cognitive abilities in the subject. Another synonym is "dullards," which suggests a lack of mental sharpness or quick wit. "Simpletons" is another option, indicating a lack of complex thinking or sophisticated understanding. Ultimately, all of these synonyms convey a similar idea: that the subject is perceived as unintelligent or obtuse.