Hi dscottr,
Thank you for participating in the Apple Support Communities. We understand your storage space keeps filling up after you delete things on your iPhone. Oftentimes this can be because you have more photos and videos store in iCloud than can fit on your device. So you when you delete some data on your iPhone, iCloud will sync more photos to your device. You may consider turning on "Optimize iPhone Storage" in Settings > Photos. This article explains more about this: Manage your photo and video storage - Apple Support.
"Store your photos and videos in iCloud
By default, your photos and videos are stored on your device in their original, high-resolution version. This means that they use a lot of space on your iPhone, iPad, and iPod touch. With iCloud Photos, you can make more space available on your device and still have access to your entire full-resolution collection wherever you go.
Get started with iCloud Photos:
- Tap Settings > [your name] > iCloud > Photos.
- Tap Sync this iPhone. In iOS 15 or earlier, tap to turn on iCloud Photos.
- Select Optimize iPhone Storage to save space on your device.
When Optimize Storage is turned on, full-resolution photos and videos are stored in iCloud, and, when needed, space-saving copies are stored on your device. And as long as you have enough space in iCloud, you can store as many photos and videos as you want."
Take care.