diff --git a/mercurial/interfaces/repository.py b/mercurial/interfaces/repository.py
--- a/mercurial/interfaces/repository.py
+++ b/mercurial/interfaces/repository.py
@@ -18,6 +18,10 @@
 # Enables sparse working directory usage
 SPARSE_REQUIREMENT = b'exp-sparse'
 
+# Enables the internal phase which is used to hide changesets instead
+# of stripping them
+INTERNAL_PHASE_REQUIREMENT = b'internal-phase'
+
 # Local repository feature string.
 
 # Revlogs are being used for file storage.
diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -1068,7 +1068,7 @@
         b'relshared',
         b'dotencode',
         repository.SPARSE_REQUIREMENT,
-        b'internal-phase',
+        repository.INTERNAL_PHASE_REQUIREMENT,
     }
 
     # list of prefix for file which can be written without 'wlock'
@@ -3324,7 +3324,7 @@
         requirements.add(REVLOGV2_REQUIREMENT)
     # experimental config: format.internal-phase
     if ui.configbool(b'format', b'internal-phase'):
-        requirements.add(b'internal-phase')
+        requirements.add(repository.INTERNAL_PHASE_REQUIREMENT)
 
     if createopts.get(b'narrowfiles'):
         requirements.add(repository.NARROW_REQUIREMENT)
diff --git a/mercurial/phases.py b/mercurial/phases.py
--- a/mercurial/phases.py
+++ b/mercurial/phases.py
@@ -125,6 +125,7 @@
     txnutil,
     util,
 )
+from .interfaces import repository
 
 _fphasesentry = struct.Struct(b'>i20s')
 
@@ -154,7 +155,7 @@
 
 def supportinternal(repo):
     """True if the internal phase can be used on a repository"""
-    return b'internal-phase' in repo.requirements
+    return repository.INTERNAL_PHASE_REQUIREMENT in repo.requirements
 
 
 def _readroots(repo, phasedefaults=None):