diff --git a/mercurial/subrepo.py b/mercurial/subrepo.py
--- a/mercurial/subrepo.py
+++ b/mercurial/subrepo.py
@@ -603,7 +603,7 @@
 
     @annotatesubrepoerror
     def phase(self, state):
-        return self._repo[state].phase()
+        return self._repo[state or '.'].phase()
 
     @annotatesubrepoerror
     def remove(self):