Isolated elderly woman can't answer phone

Hello, I hope this is the right subreddit for this question.

I have an elderly widowed great aunt who lives alone and refuses to move to assisted living. She moves too slowly through her house to answer the phone on time and her eyesight and arthritis makes it difficult to call people back.

As a result, she is very lonely and isolated outside of my visits and occasional visits from neighbors.

I set her up with Alexa so she could voice control her house, only to find out to my anger that while Alexa will make phone calls, it won't answer them.

I've since tried a few Bluetooth and Wi-Fi speakers to limited success.

What I want is to place her antiquated iPhone on the ground floor of her 3 story house, and have it be connected to a network of speakers on all 3 floors. I want her to be able to tell the speakers to answer the call and be able to answer and carry out those calls over said speakers on all 3 floors.

Your advice is appreciated.