A minor note in a prediction by TrendForce mentions that new iPhones coming later this year will allow the use of the Apple Pencil. Support for the Apple Pencil needs to be built into hardware of a device, and currently only recent iPad Pros and the new iPad from earlier this year support it.
No one else has speculated that iPhones will support the Apple Pencil, and it seems this is an unlikely move by Apple. But no doubt a few people, perhaps people that already own an Apple Pencil for their iPad, would find it useful to use on the iPhone as well.
Great idea, but I am noticing the Android phone pencils also store within the phone. Apple will need to do something to make the pencil more convenient to carry around.