如果发送的数据包含多于表单，如何在php中检索表单字段

I have a simple form in which the user can enter a search term:

<form class="form-inline justify-content-center" id="searchForm">
      <div class="form-group">
            <label class="sr-only text-info" for="searchTerm">Search term</label>
            <input type="text" class="form-control mb-2 mr-sm-2 mb-sm-0" name="searchTerm" id="searchTerm" placeholder="Search">
       </div>
       <button type="submit" class="btn btn-info">Search</button>
</form>

And I send the form using ajax like this:

$form = $(e.target);
    $.ajax({
        url: "searchmovielist.php",
        type: "GET",
        data: {form: $form.serialize(), username: getCookie('username')},
        success: function (response) {
            console.log(response);
        }
    });

My question is how do I retrieve the fields from the form in php if I get the form using $_GET['form']?