Open the Photos app
Select the photo
Tap Share
Choose Mail
Select a smaller image size when prompted
Save or send the smaller version
Use the Files app to compress images with a third-party app
Install a photo compression app from the App Store
Open the app and import the photo
Choose a lower quality or smaller size setting
Export the compressed photo
Use iCloud Photos with Optimize iPhone Storage enabled
Go to Settings
Tap Photos
Turn on Optimize iPhone Storage
Take photos in a lower resolution if your camera app supports it
Avoid using ProRAW or Live Photos when smaller file sizes are needed
Convert HEIC photos to JPEG only when necessary
Crop the photo to reduce file size
Resize the photo using the Shortcuts app
Create a shortcut that resizes images
Run the shortcut on the photo
Save the resized image