Forcing Update on iPhone to Pair with New Apple Watch (iPhone says its running latest iOS, but its not??)

Hi All - Please Help!!

I'm trying to get a new Apple Watch to work for my kid, but no luck so far!!!

The iPhone 6+ won't recognize or process the latest iOS update. It is currently running 12.4.8, and says its up-to-date, but I know from my other devices that 13.0 or better is available. And more importantly, what makes this really problematic is the Apple Watch I just got them won't pair with the iPhone, saying it needs to be updated to the latest version iOS.

I've tried total factory resets on the phone and Watch, but I can't get the iPhone to accept or acknowledge any available updates?!?! PLEASE HELP