I think it will never happen, or maybe after 20 years when smartphones will possess equal to ASICs power of processing, otherwise it is not possible.
Even if its possible for our smartphone to be a portable mining for crypto it will be just a handheld grenade because of the heat it will make and
the stress to its battery will just make it impossible to use.
crypto mining is already possible for phones and other devices as long as they can connect to internet or can install a software/app that will be used for mining but you were right . the device can easily heat up if you leave the miner running for a long time which can be verry dangerous because it can be explode , if not , the device can maybe malfunction due to cpu damage caused by heat . aside from that , you cant also earn a reasonable income even if you mine all day and nigh 24/7 .