With Adobe Portfolio, you can quickly add content from your Lightroom CC Collections that are synced with Lightroom mobile. Below, you can see the Project Editor Remote where you can select "Lightroom." This will open a new window that will show all of your synced Lightroom Collections.
If you have existing collections in Lightroom CC, you can simply right click on the collection you'd like to sync with Lightroom mobile and select "Sync with Lightroom mobile."
These photos will now appear in your Lightroom mobile Gallery.
If you're new to Lightroom and have never set up a Collection, it's super easy.
On the left side of the Lightroom interface, click the "+" button next to Collections.
Once you've made the Collection, right click on the folder in the Collections menu to make sure it is syncing with Lightroom mobile. If you've already imported photos, you can drag and drop them into the collection folder you've created and they'll sync with Lightroom mobile.
Once everything has synced with Lightroom mobile, you can upload it to Portfolio by clicking the Lr button in the Project Editor:
When you do that, this popup will appear:
In that popup, you should see all of your synced Collections. Click the collection you want to add photos from and then select the photos. When you click "Import," your photos will appear in the Portfolio Project you're editing.