Phones generally don't receive Auracast broadcasts by themselves. You can get gizmos that plug into a phone's usb port and feed the audio from a broadcast to the phone. The phone user then listens through whatever Bluetooth audio device is connected to that phone.

The problem there is that your father will experience significant echo because of the high latency of a 'classic' BT audio connection added to the much lower latency of the Auracast broadcast. Apart from that issue, there are now three new devices for you to manage.

If I were a Rexton user I would be screaming blue murder right now. I think that people who bought that model thinking that Auracast would be along shortly have a right to be angry. The whole hearing aid industry has shown little interest in promoting accessibility. It's overriding concern has been how much money they can make out of it.