I have an Android 4.x phone, which when connected to a Windows PC, shows up as a device.
Is there any software solution to expose it as a drive instead?
That can be done through any app that allows you to run an FTP server on the Android phone. Two examples are:
Start a server on any of these apps, note the resulting IP address, then type it with
\\ in the
map network drive window in Windows Explorer after choosing a drive letter: