EC-CUBE 4.2.3 
サーバーOS Linux 6.1.0-18-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.1.76-1 (2024-02-01) x86_64 
DBサーバー SQLite version 3.40.1 
WEBサーバー symfony-cli/5.8.14 
PHP 7.4.33 (Core, date, libxml, openssl, pcre, sqlite3, zlib,  bcmath, bz2, ctype, curl, dom, hash, fileinfo, filter, ftp,  gd, SPL, iconv, intl, json, mbstring, session, standard,  pcntl, mysqlnd, PDO, pdo_mysql, pdo_pgsql, pdo_sqlite, pgsql,  Phar, posix, readline, Reflection, mysqli, shmop, SimpleXML,  soap, sockets, exif, sysvsem, sysvshm, tidy, tokenizer, xml,  xmlreader, xmlrpc, xmlwriter, xsl, zip, cgi-fcgi, Zend  OPcache, xdebug) 
User Agent Mozilla/5.0 (X11; Linux x86_64; rv:109.0) Gecko/20100101 Firefox/115.0

public function buildForm(FormBuilderInterface $builder, array $options)
    {
        //国際電話番号フレフィクスフィールド
        $builder->add('international_phone_number_prefix', ChoiceType::class, [
            'placeholder' => 'common.select__unspecified',
            'choices' => $this->CountryChoices,
            'required' => true,
        ]);

<dl>
                                <dt>
                                    <label class="ec-label required">{{ '国番号'|trans }}</label>
                                    <span class="ec-required">{{ 'common.required'|trans }}</span>
                                </dt>
                                <dd>
                                    <div class="ec-input">
                                        <span class="customer-form customer-international_phone_number_prefix"></span>
                                    </div>
                                </dd>
                            </dl>

<input type="hidden" id="customer-international_phone_number_prefix" class="customer-in" name="customer_international_phone_number_prefix" value="{{ Customer.international_phone_number_prefix }}">
                        <input type="hidden" id="customer-phone_number" class="customer-in" name="customer_phone_number" value="{{ Order.phone_number }}">

$('#customer').click(function() {
                $(edit).each(function(index) {
                    var name = $(this).text();
                    {# カスタマイズ：customer-international_phone_number_prefixクラスを持つ要素だった場合はselect型にする #}
                    {# var input = $('<input id="edit' + index + '" type="text" />').val(name); #}
                    if ($(this).hasClass('customer-international_phone_number_prefix')) {
                        var input = $('<input id="edit' + index + '" type="select" />').val(name);
                    } else {
                        var input = $('<input id="edit' + index + '" type="text" />').val(name);
                    }
                    $(form[index]).empty().append(input);
                });

                $('.non-customer-display').hide();
                $('.non-customer-edit').show();
                $('.mod-button').show();
            });