Python-build-system does not honour phases

[Andreas Enge]

Apparently, the #:phases parameter has no influence on the python build
system.

For instance, when adding
(arguments
  `(#:phases '()))
the package still gets built with the %standard-phases.

I added a line
   #:phases ,phases
to
   (define builder
at line 131 of guix/build-system/python.scm.

Now I can empty out the phases.

But when I write something like
#:phases
  (alist-replace
   'install
   ...
   %standard-phases)
apparently the %standard-phases from the GNU build system are used,
as there is an error message that ./configure is not found.

Could maybe someone have a look and propose a solution?

Andreas