@PetePot There must be something wrong with your phplist shell script because the command works for me.
php /home/duncan/www/lists/admin/index.php -p import -f /home/duncan/Downloads/import.csv -c /home/duncan/Development/PHP/phplist/config.php -l 1
But it then fails.
Error: Invalid security token, please reload the page and try again
Instead you can try the Subscribers plugin, to which I have added a command line page that uses the core phplist processing, see https://resources.phplist.com/plugin/subscribers#import_from_the_command_line