The flag of languages not appear in phone burger menu.

besides that : this is the shortcode for polylang lang switch:

function custom_polylang_langswitcher() {
  $output = '';
  if ( function_exists( 'pll_the_languages' ) ) {
    $args   = [
      'show_flags'    => 1,
      'hide_if_empty' => 0,
      'show_names'    => 1,
      'echo'          => 0,
    ];
    $output = '<ul class="polylang_langswitcher">'.pll_the_languages( $args ). '</ul>';
  }
  return $output;
}
add_shortcode( 'polylang_langswitcher', 'custom_polylang_langswitcher' );

there are a lot of args you can use to manage the way it looks like:

/**
* @param array     $args {
*   Optional array of arguments.
*
*   @type int      $dropdown               The list is displayed as dropdown if set, defaults to 0.
*   @type int      $echo                   Echoes the list if set to 1, defaults to 1.
*   @type int      $hide_if_empty          Hides languages with no posts ( or pages ) if set to 1, defaults to 1.
*   @type int      $show_flags             Displays flags if set to 1, defaults to 0.
*   @type int      $show_names             Shows language names if set to 1, defaults to 1.
*   @type string   $display_names_as       Whether to display the language name or its slug, valid options are 'slug' and 'name', defaults to name.
*   @type int      $force_home             Will always link to home in translated language if set to 1, defaults to 0.
*   @type int      $hide_if_no_translation Hides the link if there is no translation if set to 1, defaults to 0.
*   @type int      $hide_current           Hides the current language if set to 1, defaults to 0.
*   @type int      $post_id                Returns links to the translations of the post defined by post_id if set, defaults not set.
*   @type int      $raw                    Return a raw array instead of html markup if set to 1, defaults to 0.
*   @type string   $item_spacing           Whether to preserve or discard whitespace between list items, valid options are 'preserve' and 'discard', defaults to 'preserve'.
*   @type int      $admin_render           Allows to force the current language code in an admin context if set, default to 0. Need to set the admin_current_lang argument below.
*   @type string   $admin_current_lang     The current language code in an admin context. Need to set the admin_render to 1, defaults not set.
*   @type string[] $classes                A list of CSS classes to set to each elements outputted.
*   @type string[] $link_classes           A list of CSS classes to set to each link outputted.
* }
*/

some quick css:

.lang-item {
  display:inline;
  padding-left:5px;
  list-style:none;
}