You will only see that if you sync your camera roll or photos on your device, back to LR desktop. You can set Camera Roll to auto sync, going forward, every time you take a new photo with your phone camera.
Taking a photo on my tablet, I can see it on my iphone some seconds later so works perfect but nothing appear in Lr desktop...
De-installed and cleared prefs of lightroom 6.3.
Re-installed Lr6.3, Lr mobile folders and collections appeared, hourra!
Opened my old catalog, Lr mobile folders and collections disappeared!!! GRRRR...
Importing my big catalog in a new one...
Thanks for the help