There are mobile phones with very large buttons available. You can get a phone on pay as you go systems, can cost you as little as €10 each year, and they are not difficult to work.
You should go to your local library or Citizens information Centre and they will point you in the direction of somebody to show you how to operate the system
I see no reason why they cannot substitute for a land line.
If you fail to get the information you need, contact Age Action in Dublin and they will direct you to your nearest source of information. 01 475 6989
Best wishes browtal