Antonyms for the phrase "spoke highly of" could be words or phrases such as criticized, condemned, denigrated, disapproved, disparaged, downgraded, maligned, reviled, slandered, and vilified. These terms carry a negative connotation and indicate the opposite of praising or applauding someone or something. Speaking negatively about someone or something can damage their reputation and cause harm. Instead, it is always better to use constructive feedback and express concerns in a respectful and constructive manner. Choosing the right words can make a huge difference in how someone is perceived and can help maintain positive relationships.