If you are looking for a job, the odds are that the organization you are interviewing with already realizes that the situation with your former employer was not ideal. That’s perfectly fine. However, when you say something negative about your former employer, this makes you look angry, bitter and like someone who could not get along in that environment. The interviewer will wonder if you will have the same problems again if they hire you.
More importantly, it makes you look disloyal. If you say something negative about your former employer, then the interviewer will know you are likely to do the same thing to them in the future.
Learn why attorneys usually fail law firm phone-screening interviews in this article: