Can you pair the watch to two iPhones?

No, you can only pair the watch to one iPhone at a time.

You can use two iPhones, but your Apple Watch can only be paired with one iPhone at any given time. To switch between phones, you would therefore need to first unpair your watch from the iPhone that you are currently using and then pair it to the other one.

The Watch app on iPhone takes backups of the watch automatically, including a fresh backup when unpairing. Each time you re-pair, during setup you can restore the watch from the backup that is stored on that iPhone. Most data and settings will be restored, with some exclusions (eg cards used for Apple Pay on your watch, the watch passcode).

Unpair your Apple Watch and iPhone - Apple Support

Set up your Apple Watch - Apple Support