WHY ISN’T CALLER ID WORKING ON MY WATCH, EVEN WHEN I HAVE THE NUMBER SAVED IN MY PHONE?

You need to allow permission for your watch to receive information from your phone.

Android users (in general, these settings may be moved around or named differently depending on the manufacturer of your Android phone):

Settings → Privacy → Permission Manager, tap on both “Phone” and “Contacts” to make sure the Wear OS app has permission for both.
Older phones may list “Calls” or “Telephone”, make sure Wear OS has permissions for both of these as well.
It may be located under Wear OS Permissions in the Apps & notifications section of Settings
It may be located under Settings → Connected devices → Bluetooth, tap the settings icon next to your watch, and make sure to allow “Phone Calls” and “Contacts Sharing”.

Settings → Wear OS by Google app → make sure Bluetooth and Contacts are given access (at all times).
There is a chance these options might not appear if you denied access during setup. You may have to factory reset your watch and repair to get iOS to ask for the permissions again.