$posts->photos() is the relationship query to return all of the photos for a post. If you call delete() on that, it will delete…
In your migrations you can do something like:
$table->json('field_name');
And in your model you add the field to the $casts property to instruct Eloquent to deserialize it from JSON into a PHP array:
class SomeModel extends Model
{
protected $casts = [
'field_name' => 'array'
];