1) Energy is the limiting factor IF we decide to do different things than we have done so far. So far what we have done with energy is mainly deplete and destroy things. In other words: we are very clumsy in the way we control matter, we cause tremendous side effects with our actions that are going to end up swallowing us back into the abyss if we don't change.

2) Energy being the limiting factor is in itself a huge problem, given the amount of energy your problem requires: the amount of energy required to get the original quality raw materials back from an iPhone is orders of magnitude bigger than the one that was needed to extract them from nature in the first place. It seems irrational to bet on this as a means for getting to a sustainable model in the short term (30-50 years).

All natural resources are limited based on which are are alive. You might be living in a bubble in a privileged place.