It won't happen.
Smartphone for bitcoin mining? you are just destroying your phone.
Smartphone as digital wallet, you can simply download an app / wallet and that's how you make it as your wallet.
It already is happening as we speak. HTC is creating a Blockchain phone and another smart phone with such abilities already exits. Its not fully intended for mining, but it does mining apparently.
There are apps intended for mining:
https://www.techradar.com/how-to/how-to-mine-cryptocurrencies-on-your-android-smartphoneAlthouugh mining will fuck phones up, it is still possible. Phones by Razer and Asus ROG(which has liquid cooling) can do a little mining but again, is a resource drainer.