Best way to add phone service to existing AT&T Fiber account?

We've got AT&T Fiber (which we're very happy with) with the BGW320 gateway.  Now we'd like to port an existing phone number (from Charter) so that it works when I connect our home phones to the existing fiber gateway.

The main problem is that I can't find the right place on AT&T's labyrinthine website to do this.  90% of "phone" links/searches lead you to wireless stuff.  And I'm guessing the "landline" section probably isn't what I'm looking for either.  Do I need to call fiber support?  Or phone support?  Ideally I'd be able to accomplish something through a web chat; that's my top preference (with calling a support phone number in dead-last place, preference-wise).

Thanks to anyone that can point me in the right direction.