Ubuntu - Mobile Phones - Cannot View Files on Android iPhone USB File Transfer Not Working

If you plugin your phone to your computer and enable USB File Transfer/Allow on the phone side but the contents of your phone on the computer side are empty in the file manager, you probably do not have mtp-tools.

MTP or media transfer protocol is the standard protocol that most phones use to communicate over USB to the computer.

Install mtp-tools

sudo apt install mtp-tools

NOTE: After that you should be able to access the internal storage of your Apple/Android phone, but you may need to reconnect the phone first.