The iPad is using iCloud Photo Library with your AppleID? You said Shared. Shared in iCloud I'm guessing?
If you do not use the same AppleID for both devices? If you do, then you don't have to do anything if using iCloud Photo Library. Just enable that setting on iPhone. Then open the Photos app.
If you don't use the same AppleID, on your iPad, just send a Shared link email for the Shared Album to yourself to the iPhone. or you can use Air Drop from iPad to iPhone to send directly. You can send all the photos in an email from the iPad to yourself on the iPhone.