There are many words, here are a couple of them:

> phraseology<br>
> 1.the manner in which words or phrases are used<br> [Collins Dictionary][1]
> 
> 1.manner or style of verbal expression; characteristic language:<br> legal phraseology.<br> [Random House Kernerman Webster's College
> Dictionary][1]
> 
> A particular mode of expression, especially one characteristic of a
> particular speaker or subject area.<br> ‘I know that my phraseology
> and way of putting things is sometimes a bit direct.’<br> [Oxford
> Living Dictionaries][2]

There is also "register". "register" doesn't necessarily have to do with formality, class and social status, but often does, at least more often than "phraseology". It's also a bit more jargonistic, ie., specific to study of language.

> 1.(Linguistics) a form of a language associated with a particular social situation or subject matter, such as obscene slang, legal
> language, or journalese.<br> [Collins Dictionary][3]
> 
> 9.A variety or level of language used in a specific social setting: speaking in an informal register; writing in a scientific
> register.<br> [American Heritage Dictionary][3]<br>

  [1]: https://www.thefreedictionary.com/phraseology
  [2]: https://en.oxforddictionaries.com/definition/phraseology
  [3]: https://www.thefreedictionary.com/register
  [4]: https://www.thefreedictionary.com/diction