For people with Iphones, how do you keep your pics when you switch phones?

Ok so this might be a stupid question but I've never had an Iphonr and I'm just wondering how do you keep all your pictures when you switch phones or something? Cuz I keep everything on my sd card and everything got erased twice and like half my life is on there… So ya, just wondering

I prefer to just use windows explorer and cut/paste them from iphone to PC.