Is there a way to quickly redial the last number in the phone.app? I know you can go into recents but is there a quicker way on iOS 12 using iPhone SE?
There is a way. Go to phone.app and go to the keypad screen.
Then with no numbers pressed, press the green dial icon. This will automatically show the last dialled number.
This is also possible if you received the calls while locked.
Under Settings > Notifications, if you have "Show Previews" > Always along with Phone > Alerts > Show on Lock Screen, then all you have to do is tap on the missed call from the lock screen to call it back.