Syncing between C drive and phone with robocopy

I'm on Windows 10 and trying to sync my music folder with the one on my LG G5. My plan is to use robocopy /mir, but I don't know how to write out a path to the directory on my phone. The phone's set to file transfer mode, so I can navigate to it in Windows Explorer through This PC > G5 > Internal storage. But there's not a drive letter or anything so I'm not sure what the command line path is. Is this even possible?

Since someone asked, the list volume command in diskpart outputted the following:

Volume ###  Ltr  Label        Fs     Type       Size     Status     Info
----------  ---  -----------  -----  ---------  -------  ---------  --------
Volume 0     D                       DVD-ROM        0 B  No Media
Volume 1                      NTFS   Partition   350 MB  Healthy    System
Volume 2     C                NTFS   Partition   439 GB  Healthy    Boot

As you can see, the phone isn't listed.

No, this is not possible. You’re accessing the phone using MTP or PTP. They are not filesystem access protocols but rather object storage protocols. The objects just happen to have a 1:1 mapping to files on your phone.

Somebody asked a related question, How do I access MTP devices on the command line in Windows? The answer is:

Unfortunately, APIs exposed by MTP are very different from a normal filesystem APIs. Therefore exposing MTP device as a read/write filesystem is not possible.

Of course, this also applies to all GUI tools that are not explicitly MTP-aware.