My iPhone doesn’t ring with telephone calls or messages. Why not?

Phone is an iPhone 14 Pro Max with all updates applied. Some of the phone callers ring but a large number do not, going directly to voice mail or message bank. Most of the incoming messages do not ring or bleep me but go silently into my backlog of unanswered messages.

I know the iPhone is a very clever device but its first function is to be a telephone and it is not behaving at this simple level.

Does anybody have a clue as to why this may be so and what I can do to rectify it?