What is the term when a phrase means just the opposite of what it used to mean?

For phrases, I'm not sure I've heard one specifically.

But for single words, like peruse, quite, cleave, I generally see the term contranym and auto-antonym. Wikipedia has a gigantic list of other terms*, but those are the two that I think will be most readily understood.

^{* antagonym, Janus word , enantiodrome, self-antonym, antilogy, addad, contronym, autantonym}

In its blog, Oxford Dictionaries use the term "Shifted Meanings".

http://blog.oxforddictionaries.com/?s=shifted

Whilst this term can be used for any change in word meaning, it does include words like "egregious", which has become its own opposite:

"Remarkably good" to "remarkably bad".