Bitcoin mining can only be done through computers with high graphics cards, bitcoin mining on smartphones is not possible. Some time ago, I have read that there are smartphones that have the potential to produce crypto currencies and that too, I think it will take a long time. Some apps that offer bitcoin mining on cellphones must use the cryptonote algorithm, one of the cryptocurrencies (not bitcoin), which is then converted into bitcoin.
Exactly you got the point. it was good to do with mobile phone when the block difficulty was too low. but in current scenioro you have to wait for 100 years to mine a block of bitcoin from mobile phone.