You never know! With the help of nano technology we may be able to achieve smaller chips that produces as much power as a full sized mining rigs in future. I mean that is not the reality now but it may become in future. If you were 80's kid, did you ever think that you can carry a computer in your pocket? Because what computer we have seen that time was Pentium one and it required an air conditioned room to run that. Nano technology achieved that impossible and now we carry a smart phone inside our pocket.
So keep your hope high as we don't know where the technological achievements can take us!
Yes, theoretically, in the future a smartphone may have the same amount of processing power that a mining rig has now. We can see that smartphones now have much more processing power than they first computers from the 1980s that took up a whole room. You have to realize though that mining rigs typically use the best processors and video cards. This means that they are very powerful and it'll take much longer for phones to get to that level of processing power. Now it is far from practical to use a smartphone to do mining. Smartphones cost a lot of money, but a lot of that cost is due to the fact that they have to fit so much into such a small device. It's all much cheaper if you buy bigger versions. Usually you don't need your mining farm to be portable. Just get stationary hardware. It's by far the most economically viable option.