Do not Disturb option on iOS bars incoming calls. But there are still ways in which we can allow incoming calls on our iOS devices like iPhone, iPad etc. Here are the steps on How to allow calls in Do not Disturb on iPad:
How to allow calls in Do not disturb on iPad?
There is another option where you can also allow calls during Do not disturb mode settings. That option is ‘Repeated calls’. If repeated calls are turned on, a second facetime call from the same person within three minutes is not silenced and you can hear the ringtone.
The only limitation with this option is that the person should call at least the second time within three minutes. ‘Repeated calls’ option is also available under ‘Do not disturb’ under settings.