And an app on your phone that can access the music being 'served' by the DLNA server running in your router. I recommend BubbleUpnp, buy the pro version if you want all the features. It is only available for Android though, there are similar but pricier alternatives available in iOS.
If this is a long term solution and you are serious about the content residing in your hard drive, it is advisable you invest in a NAS like those offered by Synolgy or Netgear and use WD Red hard drives for the storage or similar alternatives by Seagate. Or get a readymade solution like the WD Mycloud.
Reliability will also depend on your wifi router, as long as you are not using the absolute cheap crap ones you should be fine.