Cox doesn't make decisions about what's spam and what isn't. Webmail received from a cox.net account is treated the same as email from any other email provider. Email routed to the Spam folder was flagged as spam by an email security company before it was received by Webmail.
The only way to eliminate Webmail that's been flagged as spam is to unsubscribe from a sender within an individual spam email or delete Webmail subscriptions you've chosen to receive, if any. Subscriptions are spam generators.
Is anything in Webmail subscriptions? Settings > All settings > Accounts > Subscriptions