problem hearing incoming calls to iPhone XR iOS 16.6

I need to hear incoming calls from my own landline as it is the only way my disabled husband can call me for urgently needed help. I therefore need max ringer sound, which will over-ride volume from music or audio books or BBC sounds.. This works well when I set the alarm for a specific time, as the alarm automatically overrides the other sounds. How can I set it up for the same behaviour from phone as for alarms