The phrase "knocking high horse" refers to someone who has a high opinion of themselves and acts superior to others. Antonyms for this phrase would be words that describe someone who is humble, modest, and down-to-earth. These might include terms like unassuming, meek, unpretentious, or even self-effacing. Other possible antonyms could be words that signify someone who is considerate and respectful of others, like gracious or courteous. Alternatively, antonyms could describe people who are genuinely confident and self-assured, but not in a way that is dismissive of others, such as self-assured, confident, or poised.