Phillip Phillips is deep in the doghouse with "American Idol" ... which says he owes them a ton of cash, and he's been holding out on them for years.

19 Entertainment, which produces 'Idol,' also manages Phillips and the other winners. According to the suit filed against Phillips ... he's not paying up for 19's managerial services. The company says he's withholding about a million bucks -- and they want it now.

In the docs, obtained by TMZ, 19 says the 2012 'Idol' champ stopped paying management fees when he filed a 2015 complaint with the Labor Commission -- begging out of his contract, claiming it violated California law.

That dispute hasn't been settled -- it was delayed when 19 filed for bankruptcy earlier this year. The company thinks Phillips should pay up the money now because it still has a valid contract with him until a court says otherwise.