If you have enough iCloud storage and the setting turned on, you don’t have to put the photos anywhere. Your iPhone will upload everything on the Photos app to your iCloud account and keep a low-res proxy on your iPhone that takes way less space. You don’t delete anything. When you need to see a certain photo or video, just tap on it like you would usually do as if it was in your phone and it will be downloaded from your cloud. Everything’s automatic, you don’t even have to think about it ever again.

My entire photos and videos collection is almost 60Gb but it’s only taking 1Gb on my iPhone. If I ever need to take a look at an older photo, I just go to the photos app and tap on it and after like 1 second it’s already there like if it was always on my phone, it’s great!