mirockDon't you think first we have to define the notion of the word "idiom"
What do you mean when using this word.
For examplre, in a dictionary I found the following definitions
1) a group of words whose meaning cannot be predicted from the meanings of the constituent words, as for example (It was raining) cats and dogs
2) linguistic usage that is grammatical and natural to native speakers of a language
3) the characteristic vocabulary or usage of a specific human group or subject
As you can see people would keep in mind different definitions for the same phenomenon.
I think about idioms as about something that are comonly used by native speakers and could be defined as "standard phrases". Those phrases sometimes could be translated into Russian word-for-word, but in most cases they have their unique meanings and should be remembered as when you change a word in them they couldn't be understood, or it would make some difficulties in understanding.
I usually say that I don't use any idioms, but it isn't actually true. I just don't think about their usage and I use them even in this writing, but I could change some words in them and they cease to be clean idioms and become Runglish
(by the way - I do the same with any idioms in any language including Russian
)
PS: phrasal verbs may be considered idioms
Eg. wake up, get up, go on, go up, etc.