I am unable to pair my watch with my phone

Is the Watch new bought from Apple?

Read here => Get started - Apple Support

Is the Watch second hand?

The previous owner must first unpair from their iPhone

Read here => Sell, give away, or protect a lost Apple Watch - Apple Support

You can also provide us which iPhone and iOS version and Watch Series and watchOS version you have.

Start here;

Set up and pair your Apple Watch with iPhone - Apple Support