The year is 2300. The iPhone 279 is released, which is better than the iPhone 278. It's also smaller, and both the 278 and 279 are perfectly recyclable. Even more importantly, the apps available for both have improved over the past year.

Voila, continuing exponential growth.

We can't have exponential population growth, but infinite exponential economic growth? Dollars are just numbers in a computer. Increased economic growth can mean better resource usage rather than more resource usage.