What is the correct phrase: de petites chambres or des petites chambres? I believe that de petites chambres is the corrected version, but why?
Both are correct, it depends on what you want to say (and usage, too, to some extent). Using
de here is an undefinite article, contraction of
de des: you are talking about small rooms in general. Using
des here is a definite article, contraction of
de les: you are talking about some specific, identified small rooms.
Examples of padbrest in the other answer are great illustrations of that difference.