It's used pretty much the same way that الله يسمع منك (allah yesma' minek) "may God hear you" is used. You can reply with this phrase whenever someone says something that you want to happen. You're basically saying that you hope God/heaven will hear what the person just said and make it come true. The phrase is at least used in Syrian, Lebanese, Jordanian, and Palestinian, but I don't know if it's used elsewhere. I have 2 example clips to help with pronunciation and to give some context.
- In this first one the man and the women are complaining about making too much money. The man says that he heard the government is going to lower wages and then the woman responds من تمك لأبواب السماء.