iPhones were a type of mobile phone on 21st century Earth. Patricia Menzies mentioned them to the Sixth Doctor. (AUDIO: The Crimes of Thomas Brewster)
Clara Oswald had an iPhone. (TV: The Time of the Doctor, Deep Breath, Dark Water, Under the Lake, Before the Flood, The Woman Who Lived, The Zygon Invasion) During the Twelfth Doctor's imprisonment in the Prison, Clara's iPhone was incinerated. (PROSE: The Blood Cell) Clara obtained another and, in her form, Bonnie used the phone for numerous things. (TV: The Zygon Inversion)
The members of the Coal Hill Year 8 Gifted and Talented Group all had iPhones. In the 21st century, when Earth had become overrun with trees, they used Samson's to take selfies. (TV: In the Forrst of the Night)
The Doctor also had an iPhone, which he used to call Clara multiple times. (TV: The Zygon Invasion, The Zygon Inversion)
Courtney Woods had an iPhone, and she used it to post pictures of the Twelfth Doctor on the Moon onto Tumblr in the year 2049. Clara Oswald noted that to the Doctor. Even though he said she couldn't just put pictures of him online he was later able to use the online pictures via her phone to lead her back to him in the TARDIS. (TV: Kill the Moon)
Missy had an iPhone-like device, which could do everything an iPhone could do but could also murder people. (TV: Dark Water, Death in Heaven, The Magician's Apprentice)
Some used the iPhone to take selfies. (TV: In the Forest of the Night, The Woman Who Lived)
Other similarly named devices from that era included the iPad and the iPod. (TV: Dark Water, A Day in the Death)