I know if I’ve forgotten my phone because the start up screen on my infotainment centre will try to launch Apple CarPlay and will continue doing so until it finds the phone. The phone connects in seconds so I’m more or less alerted the phone is not with me. That said the last thing the stroke hospital advise me on on leaving them after D-Day was always carry my phone so its always in my pocket except while I sleep at night.
I also get the message to remember to take my phone with me when leaving the car but as said its normally in my trouser pocket however if I’m out in the country where weak phone signals lurk I put the phone in a little storage area on top of the dash and because I’ve seen the “don’t forget your phone” message so many times I’ve come to ignore it so always forget it but lucky you can’t see it from outside the car. It’s not long anyway until I notice my trousers aren’t falling down because of the lack of weight of the phone in pocket so making a quick return to the car.