“When you think of a cryptocurrency mining rig, it’s easy to associate it with large rigs featuring multiple GPUs in some type of air-cooled room. While that may be true, not every cryptocurrency needs hulking GPUs and rigs designed specifically with mining in mind. In fact, thanks to a handy app called MobileMiner, it’s even possible to mine certain cryptocurrency from a device as diminutive as the iPhone in your pocket.”
9to5Mac has described how to mine crypto currencies with an iPhone. You have to jailbreak the phone, but if that’s okay, take a look at the video. There is an article you can read too.
Hands-on: MobileMiner – how to mine cryptocurrency on an iPhone https://9to5mac.com/2017/12/21/hands-on-mobileminer-how-to-mine-cryptocurrency-on-an-iphone-video/