I think mostly just the iPhone exploded it, and also made a lot of things much more low effort. Like take for example people constantly posting photos of themselves and food and what have you on social media - pre iPhone high quality photos required a separate camera and a computer in order to upload onto social media. Post iPhone you could do it all from one device.
> Why iphone? We had internet on mobile phones before that point.
Certainly not in any way that mattered, and I say this as someone who spent the middle part of my career specifically on mobile.
I mean, sure, there was stuff like WAP, and some other niche phones that could (very, very clunkily) display full HTML. But the launch of the iPhone is what first brought the mobile Internet to the masses (and pretty much all smartphones after the iPhone aped the basic design), and most importantly, was the beginning of the change where websites started even giving a shit about mobile clients ("Mobile first" design and all that).