Turn on Priority Calling

If you have multiple phone lines, you can make calls with the phone line you want using the Priority Calling feature. With Priority Calling, you can assign a phone line or app to use when you make calls.
  1. In the Phone app, swipe down from the top of the screen.
  2. Tap the Settings icon > Priority Calling.
  3. Set the Use Priority Calling switch to On.
To choose your phone line when you make a call, on the Calls screen, tap the Select Line drop-down list. To use a specific phone line, tap a phone line. To automatically use your mobile line when you're connected to a mobile network, tap Use the Priority Line.