Press Sauté; cook bacon in Instant Pot® until crisp. Remove to paper towel-lined plate. Add potatoes, leeks, water, salt and pepper to pot; mix well.
Secure lid and move pressure release valve to Sealing position. Press Manual or Pressure Cook; cook at high pressure 5 minutes.
When cooking is complete, press Cancel and use quick release.
Press Sauté; add 1/2 cup milk and butter to pot. Cook and stir 1 minute, mashing potatoes until still slightly chunky. Add remaining 1/2 cup milk and cabbage; cook and stir 2 to 3 minutes or until cabbage is wilted. Stir in bacon.