Facebook tab not showing on iPhone

I recently added a form (Order Valuation (tab))to my facebook account, however the tab for the form does not show on an iphone, only on desktop?

Unfortunately, Facebook does not support Tabs on the mobile website.

What you can try is adding a direct form link as a Contact Us button on your Facebook page.

Alternatively, this is possible to embed the form with a 'Static HTML: iframe tabs' Tab App:

Adding a form to Facebook (Custom iFrame App)

They provide a special Tab link for mobile devices.

Then, you can also use that mobile Tab link as the Contact Us button link.

If you need any further assistance, please let us know.