I stream my music from Google Play. My entire library is there so I have no need to store it on my iPhone, despite having 64GBs to work with.
Now, if I could somehow make it so that my videos could sit up in a cloud somewhere and be accessed by streaming (free) then I could move the 18GB of Honeymooner's videos I have on my iPhone over.
I use a network external drive (WD book live) I have 1T and I can stream right from there.