Pairing Apple Watch to new iPhone

So everything I see tells you to erase your iwatch to pair it to a new phone when the old phone is dead or lost. The problem with this is the iwatch actually has data on it you don't want to lose as after checking icloud on the old phone some of the data is missing yet is still on watch. So how do you back up the data on the watch such as contacts so you don't lose them before you erase to sync to new phone? Not sure why Apple makes this so complicated since they know people lose or damage their phones all the time.

[Re-Titled by Moderator]