Crypto mining on smartphones, yes or no?

It is doable, but definitely not recommended. One of the issues is that it requires a lot of processing power, thus destroying your batteries fast.

The second issue is that Google and Apple don’t allow on-device mining on Android and iOS hardware(you can get around that issue of course).

And last but not least, it will not be profitable. You will spend more on electricity than you will earn from mining. You will need hardware that is made for mining.