diff -r 923362010525 -r 32857300846c mercurial/subrepo.py
--- a/mercurial/subrepo.py	Tue Apr 03 00:12:29 2018 +0530
+++ b/mercurial/subrepo.py	Mon Apr 02 08:43:08 2018 -0700
@@ -603,7 +603,7 @@
 
     @annotatesubrepoerror
     def phase(self, state):
-        return self._repo[state].phase()
+        return self._repo[state or '.'].phase()
 
     @annotatesubrepoerror
     def remove(self):