I'm not sure if this is an issue with flycheck or the phpstan-flycheck
the other php flychecks don't run.
(flycheck-add-next-checker 'php 'phpstan)
That pretends it to the list of next checkers for php.
but even if I change it to append it still doesn't work. It will run all the other checkers but not get to phpspec.
If I modify flycheck.el and manually add phpstan to next-checkers of php and php-cs.
Then it works. It seems like flycheck doesn't honor the next-checkers list and they know it.