Thanks for the reply Eric_G1, unfortunately none of this has resolved the issue. As I mentioned, I have iOS 16.2 on the iPhone. I believe this is the newest version. I am also running macOS Ventura 13.1 - all up to date. Both devices are signed into iCloud with the same Apple ID.
I tried your suggestions:
"To check on tabs on the iPhone from the linked Mac, tap on the tabs button, and choose the + button. Then scroll to the bottom here and it should have pages from the Mac at the bottom here."
On my iPhone, when I tap the tabs button, then the + button and scroll down, none of the pages/tabs or tab groups from my MacBook Air are shown.
"If nothing shows there tap on the Edit button at the bottom of the start page, and see if 'iCloud Tabs' are enabled here. You may also check for the 'Recently Closed Tabs' here as well."
I checked this and found that "iCloud Tabs" was already checked/enabled. "Recently Closed Tabs" was unchecked, so I checked the box. This made no difference to the issue - tabs/tab groups still do not show on my iPhone.
Clearly something has gone wrong with either iCloud or my iPhone - it is no longer syncing tabs with my MacBook Air. Do you have any other suggestions to resolve this issue?