I know your brother's frustration when you go back and retrace your steps meticulously to find the missing article as soon as you realise it's missing....as long as you go back immediately to the last place you had it, or thought it may have ejected from somewhere, you can reassure yourself that you did your best to locate it and that someone else must have picked it up if it's not there. I have found umpteen things (including tiny diamonds that popped out of a ring; earrings, specs (broken) by doing this. But also had the ?inconvenience/frustration of going back immediately - lost car keys/dogleash/shoe-icegripper etc - to find them gone. However, by attaching a label that has phone number or War Amps tag,
https://www.waramps.ca/ways-we-help/key-tags/ I have usually got the item back by the kind scooper-upper!!
My phone - usually in rear side or middle pocket. I'll have to figure out a system though, as when I am in a foreign country biking, and pull it out with gloved fingers to check location or take a photo, it's easy for other things like specs or a small baggie to be dragged out with it unnoticed. I guess that's when a handlebar mount comes in handy, but I'm running out of landscape in the cockpit with a small frame and a bell and an Edge computer there already.