Which model had the slot? Like the original? I started with the 5 and it didn’t have one but I’ve always been hampered by the lack of space.
MacBook laptops had SD cards slots, or at least the Air and Pro models. iPhones and iPads never did, although there’s been a super awkward adapter available for iPad since it first came out, but it is super limited in what it can be used for.
Even the immense photo and video/graphics userbase of Apple wasn't enough to stop the SD card slot removal. :-(