Then your computer may not be seeing the phone correctly. Some phones do not automatically show on the computer or show their files.
When you first connect the phone to the computer, if you get a popup on the computer screen that lets you choose how you want to access it, be sure you choose the option to view the files.
If that does not show, then once the phone is connected to the computer, tap the phone screen so that you can see the phones main screen. Tap and slide down and you may see the way it is connected to the computer, with the option to tap for more options. If that is the case, or if the phone screen automatically shows you a list of options on how you will connect, then you want to choose the option to transfer/access...