<form method="post" action="debug.php">
      <div class="form-group">
        <label for="recipient-name" class="form-control-label">Recipient:</label>
        <input type="text" class="form-control" id="recipient-name">
      </div>
      <div class="">
                <div>
            <textarea class="summernote" id="m_summernote_1" name="conteudo_textarea">

            </textarea>
        </div>
            </div>

  </div>
  <div class="modal-footer">
    <button type="button" class="btn btn-secondary" data-dismiss="modal">Cancelar</button>
    <button type="submit" class="btn btn-primary">Enviar</button>
  </div> </form>

var SummernoteDemo={init:function(){$(".summernote").summernote({height:150})}};jQuery(document).ready(function(){SummernoteDemo.init()});

<?php echo '<pre>'; print_r ($_POST);  die;