Do Not Disturb lets you suppress incoming phone rings and audio alerts, even those from apps. You can schedule a recurring time for it to kick in, say between midnight and 6am in the morning, when you're in bed. For more granular control, you can decide which incoming calls shouldn't be silenced (options include everyone, no one, those in your Favorites list, or a specific contact group). There's also a Repeated Calls toggle, which when enabled will allow a second call from the same person within three minutes to ring. The assumption is it must be something important for a person to keep calling you in such a short span of time.