iPhone Why can't I delete "screenshots" from my iPhone?

[hakr100]

It turns out I have 300+ screen shots on my iPhone. I'm running the latest IOS version. I want to delete these photos. I have the iCloud save option turned off on the phone. I can "select" these photos, but the option to delete them all is greyed out. I'm not syncing photos from my iPhone to my iMac or anywhere else. There has to be a reasonable way to deleted these photos, right? So what is it?

 

[Mac... nificent]

Delete photos on your iPhone or iPad - Apple Support

You can delete a single photo or video or delete multiple images at once. You can also recover anything that you accidentally delete.

support.apple.com