Hello GrahamGellatly,
Thanks for reaching out to the Apple Support Communities! I understand that you're no longer seeing the suggestions of which folder you'd like to move your mail message to.
If you recently restored your iPhone, you will need to help it "learn" where your email is going to be moved to. After doing this with a few pieces of mail, you should again see the "Move to 'mailbox'" appear. I checked an iPhone 6 Plus running iOS 12.4.4 as well as an iPhone XS Max running iOS 13.3 and both devices are showing the move suggestion.
If you have not restored your iPhone, first, restart it following these steps: Restart your iPhone. Once restarted, see if there is any change. If there is not, also check to see if your iPhone 6 is running iOS 12.4.4, which is the latest iOS update for your iPhone at this time. You can check by going to Settings > General > Software Update.
Cheers!