Yes, choose All Watches at the top of the Watch app on your phone and then Add a Watch and set up your second Apple Watch.  Note, there’s a caveat. Your iPhone will assume you are using one watch at a time. Apple Watch Family Plan users have another option for multiple pairing, which allows you to pair a dependent Child's Cellular Apple Watch to your iPhone and control that Apple Watch directly from your iPhone.   An Apple Watch paired this way has limited features, because some of the features assume the Apple Watch has full access to the iPhone, and a child should not have full access to a parent's iPhone.  Of course, it does not need to be a dependent child, but that is the basic idea.