How to transfer my iPhone Music library (including custom playlists) to my Mac?

Okay,

Imagine you had your whole Music/iTunes library customly arranged into folders on your Mac, and each of those folders was meant for a playlist in your Music/iTunes. For example, "house music" is a playlist in Music on your iPhone, as well as there is a "house music" folder from which it is being located. You have 5 of those folders + another one with all the rest of miscellaneous music.

That's exactly how my music library was arranged.

Today I tried to transfer all the music (35GBs of it) from my Macintosh internal drive to an external hard drive, in order to free up the space. By doing so, I also wanted to ensure that my Music/iTunes library gets automatically located according to those changes. While doing so, I did some sort of a mistake, where all my custom folders got overwritten, therefore the folders got emptied and all the music is now mixed, combined and it will take me days to rearrange it back into folders/playlists I have been arranging them in for years.

However, this whole library of mine is still on my iPhone just in the way as I want it to be, but I am afraid I am going to lose its construction when I plug my iPhone into my Mac. How can I transfer my iPhone Music library, incl. playlist arrangements back onto the Mac Music? Keep in mind, the music files exist on my iPhone only.