The default list is denoted by the 📥 inbox icon to the right of the list name. Any cards that are texted in without a hashtag will be posted in this list by default.
navigate to the Voice Page
locate the list that you would like to designate as the default list
select the ⋮ 3 dot menu to the right of the list name
select
📥 Default List for New Cards
The default list does not have to be within the default tab. Cards that are texted or emailed in will be unaffected by the setting of the default tab.