Hi. Is there any way of telling LR to build smart previews within LR Desktop of images imported from LR Mobile? I know how to request smart previews of images imported using the Import dialogue, but if images are first created in LR Mobile, for example by using the LR Mobile camera, when the images are sync'ed with the Desktop is it possible to set things up so that smart previews are automatically build at the same time?
No, that's not possible.
You could always use a smart collection to identify photos taken with your phone and which don't have smart previews, then create them manually.