While SS forgetting her phone may sound strange to you, I am one who could be an example of how that can happen. I've done it all too often, unfortunately.
I don't use my phone all that much, and its customary place is in my purse, since if I go out, I always take my purse.
Now, my phone can go easily over a week or so without re-charging it. So, I'll have it out of the purse, charging up, wanting it to be fully charged before hitting the road. Even if I have it on my list of Things to Bring Along, I can still miss it. I'll look at the phone, see that it's still charging, and wait for the last minute---then end up forgetting it, altogether, as I busy myself with other trip details!
I've forgotten it enough times that I have started the habit of attaching a note to my purse ("Phone!") right after I plug it in for charging so I'll remember to get it before heading out.
Granted, I could be against the norm nowadays. I will bet my teen kids would never forget their phones!