It’s fairly well documented that the iPad was what he’d wanted to have for a while, well before the iPhone existed. IIRC biographies put his first concept of what became the iPad around when the iPod was released.
The iPhone was just a happy accident, something they decided to do with the cool tech they were playing with when working on the iPad, before it was ready.
The IPad was described as a glass keyboard when it was still a secret. It was inspired by an argument with a Microsoft employee who argued apple should license the windows tablet OS and make tablets.
The whole company was more focused on making a phone however. And three secret internal movements converged into what is the IPhone today. Best thing is it was kept secret from Steve Jobs. But once he saw it, he shelved the iPad and worked on the iPhone.
The iPhone's predecessor was the Motorola iTunes phone. Which was a combo of the ipod and phone.
A bit of compiled history.
Edit: iPad was a development concept because he believed tablets should not have a stylus. And got angry at Microsoft employee for suggesting it should.
