Can I safely change ICloud/Photos setting to optimise Iphone storage and not risk losing images?

I lack storage space on my iphone as a result of opting to download full original images onto my phone in my iCloud option settings. I now want to free up space on my phone by changing the ICloud setting to Optimise storage on iPhone. Can I simply change the setting to upload the originals images onto ICloud without risking losing the originals on my phone? I do not plan to delete any images.