What line of work are you in that you need to be able to use the phone? I'm just curious, not criticizing. As for me, I'm a graphic designer and all my work is computer-based, so I don't need hearing in order to do my job. That's why I was wondering what you do.
If you are certain your hearing will decrease (as you wrote in an earlier post), and phone usage is a requirement, you may need to consider a career change. It happens to many of us. You can go back to school, especially with VR support, and learn a new career. (I know I'm "glossing" over here -- it's not a piece of cake or an overnight change, it does take time, BUT .. it can happen. I went to college majoring in Business Management and minoring in Fine Arts, and after graduation, I could not find any management-style job that would hire me for the life of me because of not being able to use the phone, so I changed direction and used my Fine Arts skills and ended up being a very good graphic designer instead.)