Why won’t people answer their phones

I’m not sure why you wouldn’t leave the update as a voicemail, or send it as a message or email. Or indeed, tell your son, who can update his wife.

I answer my landline, my mobile phone rarely because the reception in my home is dreadful and speaking and being heard is erratic.
I have one acquaintance who only communicates via whatsapp and refuses to use any other form of communication because it suits her best. So be it.

Brought up in the days of landlines and obviously before caller display, my instinct is always to pick up. The daughters laugh when I preface a call to them with “is this a good time?” And reply that if it wasn’t, they simply wouldn’t answer.
I have mixed feelings on this.
It might be important, if a crisis, what is the point of leaving a voicemail? I also secretly find it discourteous to think that somebody, seeing my number/name on the display has chosen not to pick up!
But autres temps, autres moeurs

I'm with Norah. My phone is for me, not for others. It's frequently on silent, because I'm working or sleeping or unavailable. If I see a missed call from a family member, grandson's school etc, I will usually call them back.

Our personal phone for our convenience, not for convenience of others, may not get answered. My husband's business phone always gets answered.

Perhaps her phone is just for her use? Email or call your son.

I don`t answer when it is someone I don`t want to speak to and I never answer an unknown number. I google that number and more often than not it is a phishing call.

Kartush, send her a letter if the situation is important

Kartush, to be blunt, maybe take the hint and give up? If she blames you, you have a record of trying to contact her.

One DIL of mine will get in touch when it suits her - and only when it suits her. Obviously, I'm not welcomed to keep in touch - so anything important is emailed to my son (although he's very busy and she isn't).