I have a similar situation, though the phlegm has brown
flecks, as apposed to being purely brown
. If you go to search, type in "brown
flecks" it'll take you to my post (pic included).
I've been smoking much longer than you. In the past, it seemed like my lungs would "clear out" once, twice a year around Spring/Fall time. The color was brown
I hope this resolves for you. I again plan to try to quit smoking but need to get past a few hurdles first.