Hi there, the theme is set to show a drop down menu on the mobile version, which displays as a small box with menu written in, that displays the pages in a drop down list when pressed.

You can set this menu up and choose the pages to display via the wp-admin > appearances > menu. Select or create the menu you’d like to display for the mobile version and check the tick-box at the bottom of the menu page and save to set the mobile menu.