Difficulties of Seniors

The mobile phone I bought for my 85- year-old father, who is currently in a nursing home now. Are important to him only the functions Select, calls, hang up. Other functions would have to operate over the menu, which is too heavy for him as a mobile phone entry.
The phone is very small and light. It is common and wackellfrei in the charging station. The display is easy to read and in black and white.
Trouble:
The sound is something plärrig.
I suppose it is the provider / reception on site that it still lasts after dialing the number for a moment, until the ringing signal is heard (when my phone seems to me that fast, but I have another Simanbieter).
This my father is unfortunately so irritated that he always thinks it's not working.
Maybe someone here has a tip: you can automatic Wählannahme, ie without the Greens listener to push the selected number set?

I do not want to be unfair here. These difficulties are certainly more with the onset of dementia and the inexperience with mobile phones. But ultimately it is also about a retirement unit. There should already be as close as possible to the old technology, be on corded phone.