Can you figure out the meaning by defining the terms? Yes, so it's a phrase instead of an idiom.
Yes
The phrase "laid eyes on" is an idiom.
"Idom" is not a word in English, so the difference is between a word and a non-word. An idiom is a phrase that cannot be understood unless you know the idiomatic meaning already. "On edge" is an example of an idiom because you are not literally standing on an edge - you are anxious or frustrated.
An idiom is a phrase that doesn't make any sense unless you know the idiomatic definition. This phrase means exactly what it looks like, so it's not an idiom.
An idiom is a phrase that doesn't make any sense unless you know the definition. This phrase makes perfect sense, so it is not an idiom. The room became quiet.
to do nothing nothing to do
idiom
Yes it is.
yes
A phrase unique to a particular language is called an "idiom." Idioms often have meanings that cannot be derived from the individual words used in the phrase.
Stuck in a rut is a phrase, but I am not sure if an idiom is the same thing as a phrase. You may be thinking of a cliche and "stuck in a RUT" is a cliche. "Stuck in a road" is neither cliche nor idiom.
You cannot understand an idiom without knowing ahead of time what it means. A phrase is just part of a normal sentence.