为了让PHP接收一个数组，你需要多个name="deletedImages[]"元素。例如，您可以为每个新值克隆现有的.deletedImages元素：

const deleteButtons = document.querySelectorAll('.delete-resource');
const removedImagesInput = document.querySelector('.deleted-images');
const removedImagesInputParent = removedImagesInput.parentNode;
//prevent submitting empty value
removedImagesInputParent.removeChild(removedImagesInput);

deleteButtons.forEach((item) => {
    item.addEventListener('click', function () {
       item.closest('.input-photo-preview').style.display = 'none';
       //create new <input> element
       const elInput = removedImagesInput.cloneNode(false);
       elInput.value = item.getAttribute('data-image-id');
       //insert new <input> into DOM
       removedImagesInputParent.appendChild(elInput);
    });
})

否则，你需要发送JSON或逗号分隔的文本（正如你所做的那样），并在php中将其解码为一个数组，如下所示：

$deletedImages = explode(",", $_POST['deletedImages']);