How to get music from itunes on PC to an iphone 6s with 9.1? Cant get music to transfer

I am an IT engineer and software developer since 25 years. I have several pcs, macs, ipods, ipads, lunix boxes, solaris boxies - you name it, I administer it.

In 25 years my biggest challenge is Itunes. It is so unintuative that, with all my experience, I cant do the simplest of operations. My friends and family all come to me with their idevices and ask me to sync all their music. I have about 10 peoples music on my pc.

I am trying to put an album I have in my itunes library on my wife's iphone 6s running ios 9.1. I have itunes 12.0.3.44

1. I drag the album over the tiny phone icon in the top left (which I did not find for weeks, and had to google it)
2. It slides open the iphone with a list of what looks like albums and shows my dragging album with a + and "17" (17 tracks presumably) in a red circle. I drop. Looks good. Now the new album is in the list.
3. At this point, I would exect itunes to send the new content to the phone. But no. Nothing appears on the phone. No activity in the top status window of itunes.
4. Frustrated, I click on the phone icon, and get the summary, apps, music, films etc view.
5. At the bottom is a sync button, which is was not greyed out, so I pressed it. Nothing happned. Pressed it again Noting. No error, no warning nothing.
6. I closed itunes. Rebooted the computer. Rebooted the phone. Went back to step 1. This time when I get to step 5, the sync button (which I have no idea what its for, I just want to drag content), is greyed out.

Under the Music tab of the phone view in itunes, it has "Sync Music" ticked. (Although I never want to sync music, only drag and drop, which would be easy and intuative). Now this tab has to select boxes: a) "Entire music library", and b) selected playlists, artists, albums and geners". the b) option was ticked, although I want option c), "just let me drag my music onto the iphone".

So how do I get music onto the iphone? Drag and drop "seems" to work, there are no errors, but nothing gets onto the phone. The mystery and very un-apple like sync button is greyed out.

The strange thing is that I CAN drag and drop music onto my ipad, and it starts copying immediately - it just works.