Do you mean that your app could only run in phone, not in website?
Please note that:
On February 21, 2018, we announced the deprecation of the Dynamics 365 for phones Windows Phone app. Effective May 22, 2018, the Windows Phone app is no longer supported. Support for the app on Windows tablets and PCs remains unchanged. The Windows Phone app will continue to be available in the store and will be supported for Dynamics 365 apps, (version 8.2) and earlier supported versions. If you want to continue to use the Windows Phone app, you should not update to Dynamics 365 apps, version 9.0 as the Windows Phone app will not be supported with version 9.x.
No.. am creating Sales order from Power apps to D365 CRM system, i can use only GUID to create, so i need to have LOOKUP field in Powerapps TABLET screen, can you please share me how to create LOOKUP Field in Tablet Mode?