talk down to (someone)
Definition: to talk to someone in a way that shows that the speaker thinks he or she is superior to the person he or she is talking to.
E.g.1: Parents who talk down to their teenage children rarely have a peaceful life.
E.g.2: I hate the way he talks down to me – I know at least as much as he knows about it, probably more!
This phrasal verb cannot be separated.