My (68 y/o) father does not use, upgrade, or keep his cell phone with him at all. His current phone is a very old Iphone, perhaps a ver. 5, and he generally leaves it at home when he goes out to do anything, including work, the gym, or realistically anything else.
Moreover, he does not seem to understand the modern usage pattern for cell phones - when my family needs to meet up for something, he often attempts to plan complex multi step transportation processes in advance (relying on everyone being in extremely specific places at specific times). This generally leads to him badly over-stressing when someone is 10 minutes late in traffic for example, and has no way to notify him. In cases that he does have his phone, he generally only turns it on to make a call or text, then immediately turns it off before receiving a reply.
I should mention that he has a number of other social/behavioral issues that manifest themselves in similarly frustrating ways, and are clearly the result of the same underlying behavioral disorder - however this one in particular is a massive safety issue for himself and causes the entire family unnecessary grief when we cannot contact him. He is not a technically incompetent person, he has a massively successful, 40+ career as a tenured academic scientist in STEM, at a top university (yes, really).
I have tried showing him how to use his phone, downloading apps he likes, and reminding him to bring it. He will simply say things like "I didn't bring it because it was out of charge" (this one is particularly ridiculous, because it shows he doesn't understand the normal pattern is to keep your phone charged), or "no one ever needs to call me."
What are some ways I can help him understand this is completely absurd?