Dude, seriously, if you try such a thing, be ready to get a new phone. Mining bitcoin with a smartphone will first of all impact your battery life by draining and consuming your phone's energy, leading to your device getting spoilt.
No doubt, modern smartphones are more powerful than the first computer that was invented in the 1940s. But still, when it comes to Bitcoin mining, there are far more advanced and specialized computers for the job.
I'm sure you brought up this topic because phones are smaller computers, yes. But they have a limit to what they can handle.
I was thinking of a different reason why he would've to get a new phone, which has nothing to do with system requirements. Chances are that scammers offer these apps (especially in Android, which I don't use, so I don't really know) which promise convert your smartphone in a mining machine, like the OP said. If that's the case, I guess that they are simply looking for your data in reality, when it is not malware directly.
If something sounds too good to be true...