Gravity Forms placeholders using a combination of default value and "gforms-placeholder" class

gforms_placeholders.php

function enable_gforms_placeholders($content, $field, $value, $lead_id, $form_id) {
  if (strpos($field['cssClass'], 'gforms-placeholder') !== false) {
    switch ($field['type']) {
      case 'text':
      case 'phone':
      case 'website':
      case 'number':
      case 'name':
      case 'address':
      case 'email':
        $content = preg_replace('/<\s*input(.*) value=[\'"]([^\'"]+)[\'"](.*)(\/>|>\s*<\/input>)/', '<input$1 placeholder="$2"$3$4', $content);
        break;
      case 'textarea':
        $content = preg_replace("/<\s*textarea([^>]*)\s*>(.+)<\/\s*textarea\s*>/", '<textarea placeholder="$2"$1></textarea>', $content);
        break;
      default: break;
    }
  }

  return $content;
}
add_filter('gform_field_content', 'enable_gforms_placeholders', 10, 5);