Want to go offline for a while? Swipe up from the bottom edge of the screen to open Control Center, then turn on Do Not Disturb or Airplane Mode. 

Block unwanted callers. On a contact card, tap Block this Caller (you can see a caller’s contact card from Favorites or Recents by tapping the more info button). You can also block callers in Settings > Phone > Blocked. You will not receive voice calls, FaceTime calls, or text messages from blocked callers.