diff --git a/phosphor-regulators/src/phase_fault.hpp b/phosphor-regulators/src/phase_fault.hpp
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+/**
+ * Copyright © 2021 IBM Corporation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#pragma once
+
+#include <string>
+
+namespace phosphor::power::regulators
+{
+
+/**
+ * Redundant phase fault type.
+ *
+ * A voltage regulator is sometimes called a "phase controller" because it
+ * controls one or more phases that perform the actual voltage regulation.
+ *
+ * A regulator may have redundant phases.  If a redundant phase fails, the
+ * regulator will continue to provide the desired output voltage.  However, a
+ * phase fault error should be logged warning the user that the regulator has
+ * lost redundancy.
+ */
+enum class PhaseFaultType : unsigned char
+{
+    /**
+     * N phase fault type.
+     *
+     * Regulator has lost all redundant phases.  The regulator is now at
+     * redundancy level N.
+     */
+    n,
+
+    /**
+     * N+1 phase fault type.
+     *
+     * An "N+2" regulator has lost one redundant phase.  The regulator is now at
+     * redundancy level "N+1".
+     */
+    n_plus_1
+};
+
+/**
+ * Returns the name of the specified PhaseFaultType.
+ *
+ * @param type phase fault type
+ * @return phase fault type name
+ */
+inline std::string toString(PhaseFaultType type)
+{
+    std::string name{};
+    switch (type)
+    {
+        case PhaseFaultType::n:
+            name = "n";
+            break;
+        case PhaseFaultType::n_plus_1:
+            name = "n+1";
+            break;
+    }
+    return name;
+}
+
+} // namespace phosphor::power::regulators