Bam Margera finally got the green light to see his son -- this after recently crossing a huge milestone in sobriety -- and he has plans to see the boy for Christmas ... TMZ has learned.

David Glass -- the attorney repping Bam's estranged wife, Nikki -- tells us the former "Jackass" star has, indeed, been granted monitored visitation with their young son, Phoenix. We're told Bam can see Phoenix with a professional supervisor if/when he's in Southern California ... which is where Nikki lives with the kid.

As of right now, however, Glass says neither he nor his client have been informed about any potential dates for Bam to see Phoenix.

BM himself tells TMZ ... since he hasn't seen Phoenix in person for well over 200 days now, he's dead set on visiting his son right around Christmas -- which we're told happens to be the kid's birthday as well.

Bam says this is long overdue, as he claims to have only been allowed FT calls with Phoenix up until now -- and as such, Papa Bear is going to be flying into Los Angeles this month for an event and wants to spend some quality time with him. We're told Bam's coming with a sack full of presents, too, for Phoenix.

Apparently, Bam had purchased $5,000 worth of gifts for his kid -- but because of all the legal drama lately, he hasn't been able to give them to Phoenix just yet.

As we reported ... Bam recently hit over 100 days sober, which is a major win for him in so many respects. Bam tells us the judge in his divorce case has been monitoring this progress carefully -- and feels like the decision to grant him visitation is due to his sobriety.