Not sure. I manage my iPhone music through iTunes (mostly playlists). To get stuff off my iPhone (or iPods), I fiddle with the playlists or iTunes checkboxes (genre, album, artist, etc.).
It seems like you've found some incorrect instructions online via Google. Not surprising, a lot of stuff on the Internet is wrong.
You should post a link to the article/source in question rather than just say "I read online that..." so people here can comment on the specific advice that you are following.
The lack of responses may be due to the vague nature of this advice, plus the fact that you have given no detail about A.) what Mac and what version of the operating system you are running, B.) what iPhone and what version of the operating system you are running, and C.) what version of iTunes you are running and whether or not you elected iTunes on the Mac to manage your iPhone's music.
I'm not sure how much the MacBook has to do with it unless you were previously managing music on your iPhone, then let the MacBook start managing it when you plugged it into the new system. iTunes will prompt you the first time you connect an iDevice to a Mac with iTunes.
You probably would have had more interested eyeballs on this post had you put it in the iPhone section because the problem is with your phone, not with your MacBook.
Good for you for finally providing some details.
Sorry I can't help you out.
I manage my entire media library via iTunes on my Mac and have done so since the 3rd generation iPod (scroll wheel, circa 2003), long before there was any iPhone or other iOS device. Playlists aren't some ultra-secret hack or undocumented feature. They've been around way longer than the iPhone.
If I recall correctly, the original iPhone did not have a built-in music store. It could only play music that was synced from your computer's iTunes library.
If anyone here is a fuddy duddy, it's me, not you.
My Mac's iTunes manages ... etc
is iTunes on new Mac set to manually sync music?
mine is and thus can pick what I want one and off the iPod.