Now old PC is not suitable for mining. So how can you think about mining with Smartphone. I think is it a waste of

a waste of... what? Time? Money? Power?

Lol how about all of the above.

Unless you have an ASIC there is no point in mining now IMO

If you have an early generation of ASIC, the power efficiency won't be good and you will be wasting money running the miner.