Welcome kwickcut! Glad to see you made it to the forums.
CubeCart uses the PHPMailer library (https://github.com/PHPMailer/PHPMailer) for all email transportation.
PHPMailer is told to use SMTP, or to use PHP's mail() functions that relate to the connection to whatever service is defined in the PHP.INI file, which generally is a server on localhost.
So, when you say 'phpmail', do you mean PHP's mail() family of functions, or the PHPMailer library?
If in admin, Store Settings, Advanced tab, Sending Method is PHP 's mail() functions, then you do not enter anything relating to SMTP details, as the connection details to postfix (or whatever) should already be in the PHP.INI file.