Have you created Landscape only layout? if you do, iPhone supports only Portrait orientation hence it is not visible on iPhone6.
If you tried both orientations and still can't get it working on iPhone6, please drop a note at email@example.com
with following details:
- Are you using QuarkXPress or InDesign
- please confirm the version you are using.
- please email the publication name so that we can verify on the portal.
- please share the project/document for further troubleshooting