Sometimes a standard navigation just will not do, in that case we can use a select dropdown to rely on native phone UI.

Select Box Menu.php

<?php
/**
* Select Menu Menu Walker
* Add to functions.php file
*/

class SelectBox_Menu_Walker extends Walker_Nav_Menu {
  function start_el( &$output, $item, $depth = 0, $args = array(), $id = 0 ) {
    global $wp_query;
    $indent = ( $depth ) ? str_repeat( "\t", $depth ) : '';

    $classes = empty( $item->classes ) ? array() : (array) $item->classes;
    $selected = in_array('current-menu-item',$classes) ? 'selected="selected"' : '';
    $output .= '<option '.$selected.' value="'.$item->url.'">';
    $output .= $item->title;
  }
  function end_el( &$output, $item, $depth = 0, $args = array() ) {
    $output .= "</option>";
  }
}

Wordpress Select Menu Navigation.php

<?php
  wp_nav_menu(array(
    'container'   => '',
    'menu'        => 'Menu Name',
    'items_wrap'  => '<div class="show-desktop"><ul id="%1$s" class="%2$s">%3$s</ul></div>'
  ));

  wp_nav_menu(array(
    'container'   => '',
    'menu'        => 'Menu Name',
    'walker'      => new SelectBox_Menu_Walker(),
    'items_wrap'  => '<div class="show-mobile"><form><select onchange="if (this.value) window.location.href=this.value">%3$s</select></form></div>'
  ));
?>