Not sure I understand why you can't use your WiFi router?
On the PC, you must make sure that at least one directory/Folder is Shared and select whom to share it with. On windows, I just set it to the 'Homegroup'.
On my Linux laptop, it is Shared, but don't remember how I did it.
That PC is connected via a LAN connection to my ADSL modem/WiFi router
My laptop and my cellphones can all see my PCs that have shared directories/folders ( terminology )
I then use an app on the phone to copy files/pictures to the PC. It does not require any outside vendor or carrier to do so. Worst case, just hook up a spare WiFi router in the house, turn it on, and then just use it as a Sharing Helper from phone to PC.