Keep in mind that modern phones won't be mounted as a separate drive with a drive letter -- that only happened with very old phones that had a separate partition for storage (usually referred to as an "internal SD card"). As fuzzylumpkin said, you need to tap the USB connection notification and make sure MTP or File Transfer is selected. Then, in Windows File Explorer, the phone should show up in the device list.
Thank you everyone, I found what I was looking for & now the computer can see the phone.
1. I opened Settings>System>Developer Options>Default USB Configuration.
2. I then selected File Transfer. That's what we needed.
As for this being in the swipe-down Notification Panel, I see no way to place it there.
I opened Settings>System>Developer Options>Quick Settings Developer Tiles, but there is no selection. I only see:
Show Layout Bounds, Profile HWUI Rendering, Force RTL Layout Direction, Sensors Off,
Window Animation Scale, Winscope Trace, Wireless Debugging & Show Taps
But he doesn't need it in the Notification Panel anyway.
It does show up as its own device in Windows Explorer, which is what we needed.