I think the iPhone mounts under "Scanners and Cameras" and you should be able to access it using file explorer. If you must access it through cmd line, then you could try something like:
https://macroplant.com/iexplorer/tutorials/how-to-auto-mount-a-directory-on-iphone-ipad-ipod
Alternatively, some people are saying you can put the iPhone into "DFU" mode (I think Apple refers to this as recovery mode now) and windows will assign it a drive letter.
Note: I haven't tested either options as I don't have any reason to access the iPhone through a cmd prompt.