So I went ahead ahead and created a new playlist using the method you linked to. I still have local songs saved on my computer that are greyed out in the playlist on my phone. If it makes any difference. Most of these are songs that are not available through Spotify. Would I not be able to listen to these anywhere else other than my computer or when I control music on the desktop using nearby devices on my phone?
Okay I was able to make everything in the playlist available on both devices. One last thing though, I noticed that some songs (mostly local files on my computer) will play but there is no audio. Any reason why that might be? Other than that, thanks for your help.