Pictures

iCloud is not an archive service, it is a syncing service. This means if you delete a photo you sync with iCloud, it deletes everywhere, including iCloud.

Here is a link which explains how to upload your photos to your computer outside of iCloud, where they will remain --> Transfer photos and videos from your iPhone or iPad to your Mac or PC – Apple Support (UK)

Yota1 Said:

"Pictures: [...]I want my phone to be clean so I can have more space to take more photos.[...]"

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For thought...

Rather than fiddling with photos, just clear internal space. I'm sure not much is taken up, if only a couple hundred exist.

Troubleshooting iPhone Storage:

Internal storage cannot be upgraded. It is what it is. So, the maximum internal storage capacity never increases, even if you upgraded your iCloud plan. Learn More here: What's the Difference Between Device Storage and iCloud Storage? Apple Support

So, what to do...

Clear Space Using my User Tips:

• How to Clear Space from your Mobile Device, and What to Clear: - User Tip. You may have too much installed, and need to clear space. So, see my user tip: 
• How to Clear "Other" in your iPhone's Storage - Use Backup - User Tip. Caches would be being used for remembrance of application use. It is essentially the same for an iPhone. You'd backup your iPhone, and then restore your iPhone from the backup you've just created. All System Data will delete.

This link should help...

Transfer photos and videos from your iPhone or iPad to your Mac or PC - Apple Support