Hi Pamela
Presuming I understand you correctly there is a 'header-1' module position in the header area of the template (
http://demo.joomla51.com/0111/index.php/features/module-positions) which you can use to accommodate your phone number. By default this module position is disabled on the smallest screen devices however you can override this by adding the following to the Custom CSS field of your templates parameters...
.header-1 {
display: inline !important;
}
Ciarán