Your iPhone has more compute power than a supercomputer 30 years ago, after all.
In 30 years we will not have an iPhone-sized device with the power of today's supercomputers. Transistor scaling is in its final stages. We'll be lucky to get 2-3 more process nodes and that'll be it.
Even if we find a novel semiconductor that can scale 1000x better then silicon transistors (say DNA semiconductors), then we are still limited by classical computing. Meaning our most intelligent systems are still just good old statistical inference (I say still, but statistical inference is really powerful, and getting 1000s of orders of magnitude better at statistical inference means a world of amazing discoveries).
Perhaps quantum computing will enable new kinds of inference, then we will need to scale superconductors like we did transistors in the past 75 years, that is possible (not in the next 10-15 years though; 30-40 years is more realistic). However I don’t think this will lead to anything more then amazing statistical inference. People theorized artificial neural networks way back in the 1940s and we already had algorithms for it in the 1970s. I’m not aware of any algorithms, not even theoretical ones that gives us AGI, on any computing device (not even quantum computers).
In 30 years we will not have an iPhone-sized device with the power of today's supercomputers. Transistor scaling is in its final stages. We'll be lucky to get 2-3 more process nodes and that'll be it.