Unfortunately, Facebook does not allow viewing of pages apps on mobile devices.

The following page from Facebook developers explains this in detail:

Contest Factory recommends redirecting Facebook mobile users to the microsite page (all of Contest Factory's designs are responsive). To redirect to the microsite page, please follow these steps:

a) Create a post on your company or brand's Facebook page and include the promotion's microsite URL. For example: "Enter our promotion to win fantastic prizes! Click here to enter for free: (Microsite URL hyperlink). When a mobile user clicks on the hyperlink, a new browser tab will open of the promotion microsite, where they can enter.

b) Pin the post to the ‘Top of the Page’ of your Facebook page, so that mobile users will always see it for the duration of the promotion.