Phone for sight impaired? Any ideas?

Contact the Braille Institute in your area. My mother was able to get a phone with gigantic push buttons from the phone company with their help. It also had a volume control and a tone control. The only drawback to it was that it while it was a push button phone, it operated like an old dial phone and couldn't be used for any calls that needed you to "push 1 for English," etc.

You don't have to be completely blind to utilized the services of the Braille Institute. My mother has macular degeneration.

Try a good, big, chunky, heavy corded phone, and paint the speaker button a bright colour so that she can see it, and train her to answer the phone using that. It would be reasonable to ask one or two members of staff to help her at first until she gets the hang of it.

Does she wear a hearing aid?

Is anybody changing its batteries..?

This is just a guess, but you might check out phones for vision impaired, or contact a local association for vision impaired and see if they have any recommendations.   Sometimes organizations are aware of devices that can be of help.

One of my father's friends was sight impaired; he located and bought her a very large magnifier, kind of like the stands that we used when I was first working to place material to be copied, but it was a large magnifier.

Search "magnifier stands for phones".  I got some interesting hits.  It's not clear to me though whether or not these could be used for standard phones or just for smart phones.   

So I searched again and found these which seem more appropriate for a landline:

Or just search for "magnifier stands for land line phones."  

I think the basic idea might also be adapted if you're skilled with tools.   Get a stand and figure out how to attach and hold it to a landline phone.  (I'm still thinking about how to do this or I would be glad to offer suggestions!)   (I'm thinking of a base on a magnifier that allows it to stand next to a phone, with the base being held in place by the weight of the phone.  (I hope this makes sense?)

https://www.google.com/search?q=magnifier+stands+for+phones&sa=X&ved=2ahUKEwiGrtqPjrDtAhXSuVkKHbpBAqwQ7xYoAHoECA4QLw&biw=1280&bih=566#spf=1606940046349