How do i reduce storage space for iphone's photo app, in a safe way?

The point being, the user can Backup to iCloud >> Backup methods for iPhone, iPad, and iPod touch

The caveat being >>

Cloud backups

With a Wi-Fi network connection, you can back up your device using iCloud. You don't need to plug your device into a computer to back up with iCloud. 

iCloud backups include all the information and settings stored on your device that don't already sync to iCloud. iCloud backups don't include:

• Data that you already store and sync in iCloud, like Contacts, Calendars, and Notes
• Photos, if you turned on iCloud Photos
• iMessages, text (SMS) and multimedia (MMS) messages, if you sync messages with iCloud 
• Data stored in other cloud services, like Gmail and Exchange mail
• Apple Mail data
• Apple Pay information and settings
• Face ID or Touch ID settings
• iCloud Music Library and App Store content

BrotherEye wrote:

Hello Hoangmichael62,

You're on the right track with the "Optimize iPhone Storage" option, which is designed to help manage your device's storage more efficiently without losing your photos or videos. Here's how you can safely reduce the storage space used by the Photos app:

1. Backup to iCloud:

Before you change any settings, make sure that all your photos and videos are backed up to iCloud.

- Go to Settings > [Your Name] > iCloud > Photos, and ensure that "iCloud Photos" is turned on.

Sorry but the wording is somewhat incorrect

You can Sync to iCloud but not Backup to iCloud

iCloud is only Conduit to have files on iCloud while still having copies of the same files on the device

2. Optimize iPhone Storage:

- In the same Photos section of your iCloud settings, select "Optimize iPhone Storage."

- This setting will keep smaller, space-saving versions of your photos and videos on your iPhone and store the full-resolution versions in iCloud.

3. Verify Storage Space:

- After turning on "Optimize iPhone Storage," give your iPhone some time to upload any new photos or videos to iCloud and replace the local copies with optimized versions.

- You can check how much storage you have available on your iPhone by going to Settings > General > [Device] Storage.

4. Manual Deletion (If Necessary):

- If you still need to free up more space, you can manually delete photos and videos from your iPhone. However, this will also delete them from iCloud Photos.

- To safely delete without affecting iCloud, you would first need to turn off iCloud Photos syncing, but remember that this will remove the iCloud backup for any photos you delete afterward.

5. Turning off iCloud Photos Syncing (Proceed with caution):

- Go to Settings > [Your Name] > iCloud > Photos.

- Turn off "iCloud Photos." You will get a prompt asking what to do with the photos on your iPhone. Choose to keep them if you want them to remain on your device.

- After the photos are downloaded and iCloud Photos is turned off, you can delete photos from your device, and they won't be removed from iCloud.

6. Download Photos to a Computer:

- For added safety, you can download all your iCloud photos to a computer before making any deletions. You can do this via the iCloud website or by using the Photos app on a Mac.

Good suggestion and would do it myself.

Care to offer a link from Apple as to How to perform the above actions

7. Empty 'Recently Deleted' Album:

- Remember to empty the 'Recently Deleted' album in the Photos app to free up space immediately. Items in 'Recently Deleted' will continue to occupy space until they are permanently deleted or 30 days pass.

Please be careful when deleting photos and videos, especially if you turn off iCloud Photos. Once turned off, any deletions you make on your iPhone will not affect your iCloud library but also means any new photos or videos you take won't be backed up automatically.

Always ensure that you have a complete backup of your photos somewhere safe before making significant changes to your storage settings.

Warm regards. 🍏📸

The link below will provide methods for both iOS devices and macOS Computers to download all your Pictures and Videos from iCloud

Then, on the computer, Always make a Time Machine Backup  before doing any changes

Download iCloud photos and videos

Hello Hoangmichael62,

You're on the right track with the "Optimize iPhone Storage" option, which is designed to help manage your device's storage more efficiently without losing your photos or videos. Here's how you can safely reduce the storage space used by the Photos app:

1. Backup to iCloud:

Before you change any settings, make sure that all your photos and videos are backed up to iCloud.

- Go to Settings > [Your Name] > iCloud > Photos, and ensure that "iCloud Photos" is turned on.

2. Optimize iPhone Storage:

- In the same Photos section of your iCloud settings, select "Optimize iPhone Storage."

- This setting will keep smaller, space-saving versions of your photos and videos on your iPhone and store the full-resolution versions in iCloud.

3. Verify Storage Space:

- After turning on "Optimize iPhone Storage," give your iPhone some time to upload any new photos or videos to iCloud and replace the local copies with optimized versions.

- You can check how much storage you have available on your iPhone by going to Settings > General > [Device] Storage.

4. Manual Deletion (If Necessary):

- If you still need to free up more space, you can manually delete photos and videos from your iPhone. However, this will also delete them from iCloud Photos.

- To safely delete without affecting iCloud, you would first need to turn off iCloud Photos syncing, but remember that this will remove the iCloud backup for any photos you delete afterward.

5. Turning off iCloud Photos Syncing (Proceed with caution):

- Go to Settings > [Your Name] > iCloud > Photos.

- Turn off "iCloud Photos." You will get a prompt asking what to do with the photos on your iPhone. Choose to keep them if you want them to remain on your device.

- After the photos are downloaded and iCloud Photos is turned off, you can delete photos from your device, and they won't be removed from iCloud.

6. Download Photos to a Computer:

- For added safety, you can download all your iCloud photos to a computer before making any deletions. You can do this via the iCloud website or by using the Photos app on a Mac.

7. Empty 'Recently Deleted' Album:

- Remember to empty the 'Recently Deleted' album in the Photos app to free up space immediately. Items in 'Recently Deleted' will continue to occupy space until they are permanently deleted or 30 days pass.

Please be careful when deleting photos and videos, especially if you turn off iCloud Photos. Once turned off, any deletions you make on your iPhone will not affect your iCloud library but also means any new photos or videos you take won't be backed up automatically.

Always ensure that you have a complete backup of your photos somewhere safe before making significant changes to your storage settings.

Warm regards. 🍏📸

Sure.

Below is a link to an article from Apple which provides instructions on how to download photos from iCloud.

Download iCloud photos and videos - Apple Support

Thanks for the correction above.