I presume by what you have posted that you want to link across the internet to your home router then onward to the WD hard drive to access the audio files when away from home?
That is not so easy as running an app on your phone while at home. The reason is that when you are at home both the phone and the WD drive are on the same network so connecting the two is relatively trivial.
However when you are away from home the phone and WD drive are on two totally separate networks. If you knew the internet IP address of your router you could get as far as connecting to that but going any further will require some configuration of the router to allow you to access the WD drive. And of course if you can access the drive so, potentially, can any Tom, Dick or Harry Hacker as well. So you have to make the connection secure as well.
Factor in that the router internet IP address could change randomly, (unless you ask for a static address), and things start to be come less easy.