Apple's iPhone was first released all the way back in 2007. The original iPhone could be described as being the first-ever smartphone. It was revolutionary because it was a display-dominant device that lacked a number pad. Some even mocked it, saying professionals could never take it seriously. However, the iPhone is more popular than ever before.
The original iPhone released back in 2007 offered no video features and the camera had a resolution of only two megapixels. Even the camera app offered virtually no options aside from the shutter button and the ability to view images that you had taken. Considering the immense capabilities of the current iPhone 13 Pro, the leap in technology has been huge.
Right now, the iPhone is still considered the most popular camera in the world. Images it produces can be reasonably compared against high-end professional camera systems. And this goes for both video and still.
Interestingly, the most popular iPhone ever was the iPhone 6 and 6 Plus. This could be because Apple drastically increased the screen sizes for both phones. The video above from Marques Brownlee discusses how Apple had remained relatively reserved when it came to screen sizes. However, the iPhone 6 and 6 Plus changed all of that, and now, we have much larger screens in iPhone models.
This is obviously great for photographers too because it offers a larger viewfinder and offers more real estate to view the results.
The video linked above goes into detail for every iPhone released so far and discusses some of the key changes that have shaped today's current model, the iPhone 13 Pro.
The progression has been impressive, but I think my experience with them has differed slightly from Marques... I owned the original iPhone, the 3GS, 4S, 5S, 6S and now XS.
There was a very noticeable jump in photo quality from the original to the 3GS, a bigger jump with the 4, and 4S was a great camera. Not much dynamic range, but otherwise awesome. Improvements to the 5S were marginal, mostly better software, and dramatically better video capabilities. The 6S jumped to 12mp but was otherwise the same story, better software, better video. The XS was the first I owned with the tele lens, so that's cool. I think the sensor made a marginal leap in this model too.
I'm looking forward to my next upgrade, should be very substantial.