Maintaining a call barring phone from 250 miles away is not an option for me. Any system which could ring the phone unless the number is on a whitelist is also no an option.
Indeed, a call blocking phone IS the answer for most people here - not cheap though. But are provider agnostic, which is great.
I was only pointing out my requirements in case there are others who may fall into the same category looking after elderly parents' safety remotely. Basically, it does work, and well, bar the minor inconveniences. The most annoying is thing is not being able to listen to her voicemails to see if I have missed something important - but most ring again!