Fix cellNumber param name on /join

app/Http/Controllers/GuestController.php

@@ -28,7 +28,7 @@ class GuestController extends Controller
                 'nameLast' => $request->post('nameLast'),
                 'dob' => $request->post('dob'),
                 'medicareNumber' => $request->post('medicareNumber'),
-                'cellNumber' => $request->post('cellNumber'),
+                'phoneNumber' => $request->post('phoneNumber'),
                 'emailAddress' => $request->post('emailAddress'),
             ]);