Heat the oil in a dutch oven or stock pot over medium heat.
Add the sausage and onions to the pot and cook until beginning to brown, about 5 minutes, stirring occasionally.
Stir in the garlic and cook for 30 seconds more.
Add the chicken stock, cabbage, and Ro*Tel to the pot and stir well to combine.
Bring a boil, reduce to a simmer, and cook until the cabbage is tender, about 10 minutes.
Melt the cream cheese in the microwave until soft and easy to stir. Stir the cream cheese into the soup along with the cheddar and continue stirring over low heat until the cheeses have melted and the soup is creamy.
Taste and season with salt and pepper.
Notes
Be sure to use a smoked sausage with just 2 net carbs per 2 ounce serving. Many sausages are filled with carbs, so you'll want to check labels. Heating the cream cheese in the microwave helps keep it from separating when you add it to the soup. If it does separate a bit, just stir well to try to bring it back together. It'll taste the same either way.