Hi, Katie!
Thanks for stopping by the Apple Support Communities to get help with your new iPhone! After reading your post, it sounds like your pictures are taking up more storage than anticipated on the new device. We're happy to help!
If you were using iCloud Photos on your last iPhone, it's likely that you also had your picture storage optimized. This feature works with iCloud to ensure your iPhone always has available storage by uploading the original, high resolution copy of your pictures to iCloud and only storing a small, lower resolution picture directly on your phone. This way, you can still see the pictures on your phone (and download them if you want to), but the amount of storage required on the device is not as much.
Based on that, we'd recommend checking the Optimized Storage option is enabled for iCloud Photos: Manage your photo and video storage - Apple Support.
Have a great day!