I don't know if there is a native method to this, but if you're willing to spend $4 for a lifetime license, check out the Tasker app. It's probably the most powerful automation app for android. I have a profile that turns on the ringer automatically if I'm getting a call from a specific contact. But you could make it so that it turns on the ringer if you get any call, and then goes back to vibrate mode when the call is over.