Face of Apple Watch is frozen. Trying to pair with new IPhone. Old phone is erased. Help

Try a Forced Restart on the watch. Press and hold BOTH the Digital Crown AND the side button until the white Apple appears on the screen (approximately 10-20 seconds).

Then, since you're old phone is erased, you'll need to erase the watch using the Watch. Here's how:

Erase Apple Watch - Apple Support

Edit - I pasted the wrong link