For instance, is there a way for all subscribers with the same SIC code to be placed in a list together?
@PortiaMcGrath There isn’t a way to do that automatically. But if your intention is to send a campaign to only those subscribers with a particular SIC code then the Segment plugin will probably help. See https://resources.phplist.com/plugin/segment
The plugin is distributed with phplist. You just need to enable it, and also Common Plugin, on the Manage Plugins page.