Janet, Jermaine Jackson Clash Over 'Michael' Biopic, Heated Phone Call After Screening

Janet Jackson's smack in the middle of a heated battle with her brother Jermaine Jackson, and other family members, over the biopic, "Michael," and the feud all comes down to envy ... TMZ has learned.

One source closely tied to the family tells us, Michael Jackson's siblings first got into it during a phone call on the heels of the whole family getting together in L.A. last week to screen the movie, which hits theaters next month.

We're told Janet was very critical of the film, while Jermaine loudly applauded. It's worth noting Jermaine's son Jaafar stars as Michael ... but their conflict appears to run deeper than just the movie. The source says, "Janet's always been insanely jealous of Michael, and her career is in the toilet."

Janet -- who is, by far, the second most successful Jackson -- was the only person who reacted negatively after the family's preview, according to our source ... who added, even Janet's boyfriend cheered and said, "Now that's a movie."

We're told the other family members, including matriarch Katherine Jackson, loved it ... and Page Six reported most of the fam is team Jermaine when it comes to the project.

Of course, the movie was produced by the Michael Jackson estate, but Janet did not participate ... nor is she featured in the movie. Our source says Janet was offered an opportunity to join the production, but declined.

As for her being left out of the script ... we're told it would only have been a "bit role," anyway.