Hello Chancinit139,
We understand your iPhone isn't ringing as it should since syncing your Apple Watch and phone together. We'd like to share a variety of troubleshooting steps for you to try.
Make sure that Do Not Disturb isn't on. Both on the iPhone and Bedtime settings:
Use Do Not Disturb on your iPhone, iPad, and iPod touch - Apple Support
Use Bedtime to track your sleep on your iPhone - Apple Support
Make sure that Silence Unknown Callers hasn't been turned on. Also, if you're using an app to filter/detect spam calls, turn off all of the application's features, then remove the app(s) and restart your iPhone: Detect and block spam phone calls - Apple Support
Block phone numbers, contacts, and emails on your iPhone, iPad, or iPod touch - Apple Support -- If this is only happening with one or a few contacts, make sure they haven't been accidentally blocked.
Make sure that the iOS on your iPhone is up to date along with the carrier settings. If your iPhone needs to be update, please be sure to have a recent backup before you begin:
About the LTE options on your iPhone - Apple Support -- One last thing. If your carrier supports it, make sure that VOLTE is turned off under Settings > Cellular > Cellular Data Options > Voice & Data.
Please let us know the results when you're able.
Thanks for posting in the Apple Support Communities forum.
Have a great week!