Fixed PHP interop tests
diff --git a/src/php/lib/Grpc/ActiveCall.php b/src/php/lib/Grpc/ActiveCall.php
index 836a4b0..e0ea43a 100755
--- a/src/php/lib/Grpc/ActiveCall.php
+++ b/src/php/lib/Grpc/ActiveCall.php
@@ -28,9 +28,9 @@
     $this->flags = $flags;
 
     // Invoke the call.
-    $this->call->start_invoke($this->completion_queue,
-                              CLIENT_METADATA_READ,
-                              FINISHED, 0);
+    $this->call->invoke($this->completion_queue,
+                        CLIENT_METADATA_READ,
+                        FINISHED, 0);
     $metadata_event = $this->completion_queue->pluck(CLIENT_METADATA_READ,
                                                      Timeval::inf_future());
     $this->metadata = $metadata_event->data;