where are devices on finder I can't get my Mac to see my phone is plugged into it

It should appear in the Locations section of the Finder sidebar. See: Back up and restore your iPhone or iPad on Mac or iCloud - Apple Support

If it doesn't appear, see the following: If your device doesn’t appear in the sidebar when connected to Mac - Apple Support

System identified you as on macOS Mojave, is that right?

If yes, Mojave still uses iTunes for the job. Finder took the wheel in Catalina What happened to iTunes? - Apple Support

Good point -- I saw 10.14 in the signature and thought "Catalina" -- my memory for version numbers isn't what it ought to be!

😂 don't worry, you're not alone. I keep googling for version numbers all the time. Also need to search for the feature's announcement and articles from the past to make sure what is what 😂