Photos takes up 10gb on my phone but only 805mb on ipad

I have the optimize photos setting on but its still not optimizing. i tried turning off icloud sync on my phone and deleting all of my photos, but now it still shows 9.69GB storage even though I have 0 photos. why is it taking up so much storage? i only have 1.2k photos normally and no long videos. how do i make the photos app take up as much storage on my phone as it does on my iPad?