'Local File' folder on iPhone doesn't include all the songs that are downloaded on my phone

[okay_lydia]

There are songs that I have on my iTunes library on my phone (as well as on my computer) that just flat out don't even show up when you search for them in the Local Files folder on my iPhone. When I try adding them to playlists and things on my computer, even if both are available online and connected to the same wifi, they simply show up as greyed out and unplayable (on my phone, not on my computer). What should I do to be able to play them on my phone? I've transferred files from iTunes to Spotify before no problem, but I've never had a song on my iPhone iTunes that didn't even register in my iPhone Spotify Local Files. Sorry this is so confusing!!