Q: How do I get pictures that were on my iCloud back on my iPhone?

Not enough info. How were they put on iCloud? Unless you are using iCloud Photo Library (which would already have the photos on your device), then you cannot really "put" photos on iCloud. Can you explain what you mean?

Cheers,

GB

If they are in iCloud Photo Library you can turn on Settings > iCloud > Photos > iCloud Photo Library. If you aren't sure that you were using iCloud Photo Library you can use a computer and go to https://www.icloud.com/ and click on the Photos app to see if they are there.

The other possibility is that you did a backup to iCloud. If so you can restore the backup to your phone but be aware that the backup will completely replace the data (including photos) that is currently on your phone. iCloud: Restore or set up your iOS device from iCloud