This is unfortunately accurate, at least, for those with dementia. They need to already know how it works otherwise it's just not happening. imho the solution is skeuomorphism i.e. make the experience as close as possible to that of a landline phone made ~30 years ago. Tie it to a physical phone book with their main contacts written in a large font. (They don't necessarily need to key in the full numbers each time, a carer can pre-program "speed dial")

Have any unknown/invalid numbers go through to a default primary point of contact.