diff --git a/.circleci/config.yml b/.circleci/config.yml
index 9d4b135..3c0c8c6 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -91,7 +91,7 @@ workflows:
               only:
                 - develop
                 - security
-                - PM-3327
+                - PM-3351
 
       - "build-qa":
           context: org-global
diff --git a/app-constants.js b/app-constants.js
index 0c6f361..5c8d576 100644
--- a/app-constants.js
+++ b/app-constants.js
@@ -151,6 +151,14 @@ const PhaseFact = {
   UNRECOGNIZED: -1
 }
 
+const PhaseChangeNotificationSettings = {
+  PHASE_CHANGE: {
+    sendgridTemplateId: config.PHASE_CHANGE_SENDGRID_TEMPLATE_ID,
+    cc: [],
+  },
+};
+
+
 const auditFields = [
   'createdAt', 'createdBy', 'updatedAt', 'updatedBy'
 ]
@@ -168,4 +176,5 @@ module.exports = {
   SelfServiceNotificationSettings,
   PhaseFact,
   auditFields,
+  PhaseChangeNotificationSettings,
 };
diff --git a/config/default.js b/config/default.js
index cc0da6e..93e524f 100644
--- a/config/default.js
+++ b/config/default.js
@@ -133,4 +133,6 @@ module.exports = {
   RESOURCES_DB_SCHEMA: process.env.RESOURCES_DB_SCHEMA || "resources",
   REVIEW_DB_SCHEMA: process.env.REVIEW_DB_SCHEMA || "reviews",
   CHALLENGE_SERVICE_PRISMA_TIMEOUT: process.env.CHALLENGE_SERVICE_PRISMA_TIMEOUT ? parseInt(process.env.CHALLENGE_SERVICE_PRISMA_TIMEOUT, 10) : 10000,
+  CHALLENGE_URL: process.env.CHALLENGE_URL || 'https://www.topcoder-dev.com/challenges' ,
+  PHASE_CHANGE_SENDGRID_TEMPLATE_ID: process.env.PHASE_CHANGE_SENDGRID_TEMPLATE_ID || "",
 };
diff --git a/src/common/helper.js b/src/common/helper.js
index a7453fb..d9e3ef9 100644
--- a/src/common/helper.js
+++ b/src/common/helper.js
@@ -1638,6 +1638,72 @@ async function sendSelfServiceNotification(type, recipients, data) {
   }
 }
 
+/**
+ * Build payload for phase change email notification
+ * @param {String} challenge Id
+ * @param {String} challenge name
+ * @param {String} challenge phase name
+ * @param {String} operation to be performed on the phase - open | close | reopen
+ * @param {String|Date} at - The date/time when the phase opened/closed
+ */
+function buildPhaseChangeEmailData({ challengeId, challengeName, phaseName, operation, at }) {
+  const isOpen = operation === 'open' || operation === 'reopen';
+  const isClose = operation === 'close';
+
+  return {
+    challengeURL: `${config.CHALLENGE_URL}/${challengeId}`,
+    challengeName,
+    phaseOpen: isOpen ? phaseName : null,
+    phaseOpenDate: isOpen ? at : null,
+    phaseClose: isClose ? phaseName : null,
+    phaseCloseDate: isClose ? at : null,
+  };
+}
+
+
+/**
+ * Send phase change notification
+ * @param {String} type the notification type
+ * @param {Array} recipients the array of recipients emails
+ * @param {Object} data the data
+ */
+async function sendPhaseChangeNotification(type, recipients, data) {
+  try {
+    const settings = constants.PhaseChangeNotificationSettings?.[type];
+
+    if (!settings) {
+      logger.debug(`sendPhaseChangeNotification: unknown type ${type}`);
+      return;
+    }
+
+    if (!settings.sendgridTemplateId) {
+      logger.debug(
+        `sendPhaseChangeNotification: sendgridTemplateId not configured for type ${type}`
+      );
+      return;
+    }
+    const safeRecipients = Array.isArray(recipients) ? recipients.filter(Boolean) : [];
+
+    if (!safeRecipients.length) {
+      logger.debug(`sendPhaseChangeNotification: no recipients for type ${type}`);
+      return;
+    }
+
+    await postBusEvent('external.action.email', 
+      {
+        from: config.EMAIL_FROM,
+        replyTo: config.EMAIL_FROM,
+        recipients: safeRecipients,
+        data: data,
+        sendgrid_template_id: settings.sendgridTemplateId,
+        version: 'v3',
+      }, 
+    );
+  } catch (e) {
+    logger.debug(`Failed to post notification ${type}: ${e.message}`);
+  }
+}
+
 /**
  * Submit a request to zendesk
  * @param {Object} request the request
@@ -1756,6 +1822,8 @@ module.exports = {
   setToInternalCache,
   flushInternalCache,
   removeNullProperties,
+  buildPhaseChangeEmailData,
+  sendPhaseChangeNotification
 };
 
 logger.buildService(module.exports);
diff --git a/src/services/ChallengePhaseService.js b/src/services/ChallengePhaseService.js
index 507eb2f..4c6c4da 100644
--- a/src/services/ChallengePhaseService.js
+++ b/src/services/ChallengePhaseService.js
@@ -813,9 +813,74 @@ async function partiallyUpdateChallengePhase(currentUser, challengeId, id, data)
     _.assignIn({ id: result.id }, data)
   );
   await postChallengeUpdatedNotification(challengeId);
+
+  // send notification logic
+  try {
+    const shouldNotifyClose = Boolean(isClosingPhase);
+    const shouldNotifyOpen = Boolean(isOpeningPhase); // includes reopen
+
+    if (shouldNotifyClose || shouldNotifyOpen) {
+      // Single template - single type
+      const notificationType = "PHASE_CHANGE";
+
+      const operation = shouldNotifyClose
+        ? "close"
+        : (isReopeningPhase ? "reopen" : "open");
+
+      const at = shouldNotifyClose
+        ? (result.actualEndDate || new Date().toISOString())
+        : (result.actualStartDate || new Date().toISOString());
+
+      // fetch challenge name
+      const challenge = await prisma.challenge.findUnique({
+        where: { id: challengeId },
+        select: { name: true },
+      });
+
+      const challengeName = challenge?.name;
+
+      // build recipients
+      const resources = await helper.getChallengeResources(challengeId);
+
+      const recipients = Array.from(
+        new Set(
+          (resources || [])
+            .map(r => r?.email || r?.memberEmail)
+            .filter(Boolean)
+            .map(e => String(e).trim().toLowerCase())
+        )
+      );
+
+      if (!recipients.length) {
+        logger.debug(
+          `phase change notification skipped: no recipients for challenge ${challengeId}`
+        );
+        return _.omit(result, constants.auditFields);
+      }
+
+      // build payload that matches the SendGrid HTML template
+      const phaseName = result.name || data.name || challengePhase.name;
+
+      const payload = helper.buildPhaseChangeEmailData({
+        challengeId,
+        challengeName,
+        phaseName,
+        operation,
+        at,
+      });
+
+      await helper.sendPhaseChangeNotification(notificationType, recipients, payload);
+    }
+  } catch (e) {
+    logger.debug(
+      `phase change notification failed for challenge ${challengeId}, phase ${id}: ${e.message}`
+    );
+  }
+
   return _.omit(result, constants.auditFields);
 }
 
+
 partiallyUpdateChallengePhase.schema = {
   currentUser: Joi.any(),
   challengeId: Joi.id(),