It seems like there is a bit of confusion on what constitues a saying, an idiom, vs. slang, proverb, and so on.

phrase = 片語﹐ part of a sentence, no particular meaning behind it.

EX: "part of a sentence" is a phrase

saying = 俗語﹐ usally old bits of wisdom, often from elders or books

EX: "A stitch in time saves nine" is a saying.
俗語說﹐現在縫一針﹐省以後縫九針。

proverb = 諺語, VERY ancient saying, often racially specific. (A lot of proverbs are attributed to a specific race, like "Spanish proverb", or "Chinese proverb", and so on.)

”Do good, reap good; do evil, reap evil.“ -- Chinese proverb
"種瓜得瓜,﹐種豆得豆。”-- 中國諺語

idiom = 成語, a group of words, when used together, has a completely different meaning. Idioms are usually regional.

EX: 中國成語﹕“暗送秋波” "dark send autumn waves"?
It means stealthily making gestures of approval/seduction.

EX: American idiom: "It ain't over till the fat lady sings."
“胖女士不歌唱,這就沒完” ? (see link [to be posted])

slang = no direct Chinese equivalent, usually used in modern speech, attributed to specific groups or cultures, similar to idiom, but far more informal.

American slang: "I feel like I am going to puke."
puke = slang for "throw up, vomit"

American slang: "I gotta hit the rack by ten, man."
Translation: "I have to go to bed before ten o'clock."

And finally...

cliche = no directly Chinese equivalent term, it means something's been used so many times, it's extremely boring and old-fashioned, and stupid.

Most of the sayings and proverbs by now are considered cliches.