Photos showing on ipad but not iphone?

I recently had my iphone battery changed as it was faulty, when i got my phone back it showed as only having 1000 or so photos. All of my photos are still on my ipad and therefore in icloud, but i can’t figure out how to get them back on my phone - icloud is turned on. I was thinking it could be storage as my storage is very nearly full - but 27gb of storage on my phone is due to photos! that cannot be possible from just a couple thousand photos, i previously had around 30,000! Please can someone let me know how i can get them back on my phone.