diff --git a/cp/app/Controllers/ApplicationsController.php b/cp/app/Controllers/ApplicationsController.php
index f8970c5..d5a8c6d 100644
--- a/cp/app/Controllers/ApplicationsController.php
+++ b/cp/app/Controllers/ApplicationsController.php
@@ -74,6 +74,11 @@ class ApplicationsController extends Controller
             $authInfo = $data['authInfo'] ?? null;
             $invalid_domain = validate_label($domainName, $db);
 
+            if ($phaseType === 'custom' && empty($phaseName)) {
+                $this->container->get('flash')->addMessage('error', 'Please provide a phase name when selecting the "Custom" phase type.');
+                return $response->withHeader('Location', '/application/create')->withStatus(302);
+            }
+
             if ($invalid_domain) {
                 $this->container->get('flash')->addMessage('error', 'Error creating application: Invalid domain name');
                 return $response->withHeader('Location', '/application/create')->withStatus(302);
diff --git a/epp/src/epp-create.php b/epp/src/epp-create.php
index 4715e86..9ae2099 100644
--- a/epp/src/epp-create.php
+++ b/epp/src/epp-create.php
@@ -634,6 +634,10 @@ function processDomainCreate($conn, $db, $xml, $clid, $database_type, $trans, $m
         } elseif ($launch_phase === 'landrush') {
             // Continue
         } elseif ($launch_phase === 'custom') {
+            if (empty($launch_phase_name)) {
+                sendEppError($conn, $db, 2003, 'Missing required element: A phase name is mandatory for the custom phase.', $clTRID, $trans);
+                return;
+            }
             // Continue
         } else {
             // Mixed or unsupported form