What are some good quality phones and answering machines that would help my mother hear better on the phone as well as deciphering messages?

My 84 year old mother is becoming hard of hearing and is having a difficult time on the phone as well as hearing and understanding messages left on their answering machine. I bought a Clear Sounds answering machine for them a month or so ago and am very disappointed in the quality. It is muffled and hard for those who can hear well to make out what the message says. The slow speech setting doesn't work that well either. I'd like to get them a new phone too but wanted to reach out and see what others have used and have had success with. Also, are there any other assistive devices or products (besides hearing aids) that might help her in dealing with business transactions over the phone? It is extremely difficult and frustrating for her and she has to handle all this because my father has dementia and can no longer do any of these things. I appreciate any advice or ideas or suggestions that you all have.