A hosting plan can serve more than one domain. The Domains card on the plan's page lists every domain attached to it and which one is primary.
Attaching a domain
Type the domain into the field at the bottom of the Domains card and click Add. The domain can be one registered with phas or one you own elsewhere. A domain you own elsewhere still needs to be pointed at the plan: see Point a domain you already own at your hosting.
Attaching a domain creates the site on the server. Files for it go in the folder the control panel shows for that domain.
The primary domain
One attached domain is primary. It is the name the plan is listed under, the address used for the plan's Transactional Email sending domain by default, and the domain we use when we email you about the plan. Change it with Make primary next to any other attached domain. Nothing on the server changes; it is a label on your side.
Removing a domain
Remove next to a domain detaches it from the plan and deletes the site configuration for it on the server. The files in its folder are not deleted, so you can attach the domain again later. A domain's DNS zone is not deleted either; manage that under DNS.
You cannot remove the primary domain. Make another domain primary first.