My dad has dementia. Needs a phone to call one a few numbers. Dad is living in a memory care facility and does not have a phone in his room. He wants a phone to call mom. We want to limit the numbers he is able to call to only family members. What is available?
In my cousin's MC unit, all the person has to do is ask to speak with their family member and they will call and put them on the phone. I call my cousin several times a week and they summon her to the phone. We speak for a few minutes, as that is all she can handle. Why wouldn't that work for your dad?
You know his level, so, I'd just consider if he's able to handle a phone. If he is, he's likely to call over and over, because, he'll forget that he's already called someone a dozen times.
Maybe have it where Mom would call Dad a couple times during the day, have a set time that she would call, so he would know when to expect the call. He probably misses her a lot.
If it turns out that he calls your Mom every 10 minutes to say the same thing, then remove the phone and make up some therapeutic fib, like the telephone system is down in that part of building and it will take weeks to repair.