I am going to go against the grain of conventional advice and say you should just outline it like you did here. I have been in the position of hiring people before. I much prefer to know the real reason why someone left a company. Granted, if someone says “my boss was an asshole”, I would probably just see that as likely making excuses. But, if someone says “I left because I was subjected to verbal and emotional harassment by my boss, and if you want me to provide specific examples I can do so”, that’s actually information I would prefer to know. I think your situation falls into that later example for sure.

The idea that you should never speak ill of a former employer regardless of the circumstances IMO is bad advice.