You can't see your Lightroom Classic catalog with Lr CC and Mobile. What you can see is individual synched collections. When you create a collection, you can check the option to sync it. And existing collections have a small checkbox in front of their name all the way to the left. Images you import in LrCC and/or Mobile will automatically sync to Classic as well, images you import in Classic will only sync (as smart previews, not as full size originals) if you add them to a synched collection.