Can’t add a contact to iPhone “Favorites” list.

I saw this question before and the answers weren’t relevant in my case but I did find a simple solution that worked.

1. Write down the contact info.
2. Delete the contact completely.
3. Reenter the contact again.
4. NOW add the contact to Favorites.

Don’t know why this worked in my case. The contact may have gotten corrupted somehow.

Didn’t have to reboot when I did this but you may want to turn phone off and reboot after deleting the old contact (just before reentering it).

good luck.