Unable to get wifi sync to work between an iPhone 6 & a MacBook Pro's iTunes

Hello.

I have a newbie issue. I am trying to get sync between my work's SIMless iPhone 6 (iOS v9.3) and 15" MacBook Pro (Retina; early 2013)'s Mac OS X v10.10.5 (Yosemite; all updates including iTunes v12.3.3). I read and followed the instructions shown in https://support.apple.com/en-us/HT203075 web page, but I am not getting that Sync button in step #6. I even turned off Mac OS X's firewall. And yes, both devices are connected on the same router's guest WAP.

I did some quick Googling. They mentioned iTunes Wi-Fi Sync in iPhone's iOS. I checked there and it has a gr(e/a)yed out "Sync Now" with the the computer's name that I had connected with USB in the past.

I only see if I use the USB cable. Am I missing something?

Thank you in advance. 🙂