After several false starts, I finally figured out how to configure the DLNA server in my router to serve files from USB-attached storage to the smart TVs on my LAN. Then I installed the VLC app on my iPhone and it discovered the DLNA server immediately as a UPnP File Server in the Network tab. It works pretty well, except it doesn't show the cover art for music files. The MacOS app also discovers the server, but the interface is completely different. Overall, I'm impressed, though I did have to do some online searching to figure out how to do some basic things like random play (you have to start playing a song to access the shuffle icon).