iCloud Sync Not Working

Here is the scenario. Google syncs with my web-based law practice management software and with my Apple calendar on my Mac. That works well and fast. My old iPhone (6s) handled this well and whatever was on my Mac calendar, contacts, etc. was also always on my iPhone and iPad. I bought an iPhone X last month and laid it beside my old iPhone (6s) and set it up as instructed. The problem is that iCloud and the IOS devices are not syncing. I don't recall what might have been different with my 6s. I have read and read and tried all suggestions from several sources. All devices are signed into iCloud with the same Apple ID. Would the problem be iCloud 2 factor authentication? I don't see how since both the Mac and the IOS devices indicate that they are signed into iCloud. Any suggestions? My 2016 MacBook Pro is running V. 10.12.6 and the IOS devices are running latest upgrades. I really need help with this. Thank you. Steve