Can phplist be used with Drupal 8?
Yes, simply add your phpList installation as a Menu link. (opens as default phpList subscribe page).
If you want to customise your phpList page to be included within your Durpal site, is it possible to embed a page in Durpal? Or create a custom phpList subscribe page based on your Durpal site’s layout.
There are also Drupal modules that help with the integration of the 2 systems.
For example, to add a newsletter signup form, you can use Webform phpList. It will look like the rest of your site, whereas if you link to phpList directly, it usually looks very different, potentially spooking people.