diff --git a/tests/Zendesk/API/UnitTests/Sell/ContactsTest.php b/tests/Zendesk/API/UnitTests/Sell/ContactsTest.php
index 6e01821f..cbef554e 100644
--- a/tests/Zendesk/API/UnitTests/Sell/ContactsTest.php
+++ b/tests/Zendesk/API/UnitTests/Sell/ContactsTest.php
@@ -42,6 +42,10 @@ public function testUpsert()
 
         $encodedQueryParams = [];
         foreach ($queryParams as $key => $value) {
+            // Encode the 'phone' query param's whitespace
+            if ($key === 'phone') {
+                $value = str_replace(' ', '%20', $value);
+            }
             $encodedQueryParams[$key] = $value;
         }