replace onclick action to display inline output

i want to change the behavior of the button in this function

$STRING .= '<a href="'.$GLOBALS['CORE_THEME']['links']['author'].'/author/'.$author_info->user_login. '" class="btn btn-info btn-lg">'.$CORE->_e(array('auction','41')).'</a>';

to when clicked to display the output of this function

 $data = get_user_meta( $authorID, 'cellno', true);
        if(strlen($data) > 0){ 
        echo "<span><i class='fa fa-phone'></i> <a href='phone:".$data."' rel='nofollow' target='_blank'</a> </span>"; 

so that when " class="btn btn-info btn-lg" is clicked it will display the phone number inside it, for now it shows contact author, and opens a new page to the author page.

thanks everybody