How do I get my Father (81) to stop calling me in the middle of the day when I am at work?

I've wondered if part of it isn't that our parents spent many years without voicemail or answering machines so there's the habit of trying and trying until someone answered (maybe she's in the basement and has to run upstairs). Also part of that ingrained habit is the idea that people always answer the phone when it rings.My mom still can't get used to leaving a message and we'll call her back when we can.

Try working at home! Dad comes into my office and sits down and starts talking.... Used to be before mom died he'd call one to 2 times a day while he was driving around to keep awake... Id let it go to voicemail but the guilt would get me. I have tried the line "I am working" but that does not work all the time. I longed for a home office and now I long for an out of home office.....

My mom calls me repeatedly in the evening...as many as 6-8 calls in an hour. I let them go to voicemail, which is the only lifesaver in this situation. The other day I called her back and asked if its an emergency...she said No, why? and I told her I figured it had to be an emergency since she called so many times. She said, Well, you didn't answer. I then told her to call ONCE and leave a message and I will get back to her as soon as I can, that so many calls scares me because I think something is wrong. That tactic helped a bit but she still calls too often....boundaries, boundaries! Straight to voicemail....

Can you let his calls go to voicemail? If it's urgent or an emergency he'll say so in his voicemail.

I have a colleague with this problem. When her dad calls she says quickly "dad, is there an emergency? No, good. I'm at work, I can't talk". Click.

I understand you want to prevent the calls, perhaps someone else will have an idea about that.