Podcast-containing playlists on modern iPhone
I've been struggling with this. Although I don't have a iPhone 6, I think your problem is that you have iCloud Music Library turned on. Try turning iCloud music library off on your phone. Compile your smart playlists in iTunes and make sure "Sync podcasts" is checked and also check the smart playlists that you want to sync under "podcasts". Those smart playlists will show up in the podcasts app as a podcast station that contains all of your smart playlists. They won't, however, show up in the music app. That boat has sailed.

This has been working for me with the new iOS versions. What's not working is now that I want to try Apple Music and I turn iCloud Music Library my smart playlist station in the podcast app disappears!