diff -r 09735cde6275 -r 5d65e04b6a80 mercurial/commit.py
--- a/mercurial/commit.py	Mon Oct 19 02:54:12 2020 +0200
+++ b/mercurial/commit.py	Tue Oct 20 17:32:45 2020 +0200
@@ -105,7 +105,7 @@
             # be compliant anyway
             #
             # if minimal phase was 0 we don't need to retract anything
-            phases.registernew(repo, tr, targetphase, [n])
+            phases.registernew(repo, tr, targetphase, [repo[n].rev()])
         return n