What is the best way to teach a senior how to use an iphone?

My Great Uncle recently got a iphone 6, and he has no clue how to do anything more than make phone calls and send texts. He has been asking me to teach him how to use it, but I do not want to have to spend hours at a time teaching him about only one feature at a time. What are some good ways for me to speed up the teaching process?

Teach him how to do one thing at a time… When he needs to do it. Teaching is about presenting information in a way the student can process the information. Teaching is NOT about convenience for the teacher.

Show him the "Tips" app on the phone. It yellow with a lightbulb. My iphone 6 came with it already installed.
It has a bunch of pointers and suggestions. He can try them out himself. If he gets stuck he can make a note of it and you can help him later.

I hear you. Teaching the elderly can be extremely frustrating. Your post does not say how old your great uncle is, but I can tell you from experience that, beyond a certain age, people find technology very difficult to master. Step number one is to find out exactly what your great uncle wants to be able to do. Give up the idea of teaching him how to do everything the phone will perform, make a list of five or six functions he wants to be able to perform, and let it go at that. Step two is to take the functions "one at a time," teach him how to do ONE of them by showing him how and writing the steps down for him. Show him three or four times, then hand him the phone and let him do it. Have him perform the function five or six times "from scratch" until he is comfortable doing it. For example, you might teach him "how to turn on the flashlight." Start from the "home" screen, show him how to "swipe upward" to get the panel with the flashlight on it, and show him how to turn it on and off, and how to make the panel disappear. Then give him the phone and let him do it five or six times. When he's comfortable with it, "call it a day." Don't try to show him everything the phone will do all in one session. Quit, tell him you'll be back (whenever you normally visit), and drop the matter. Next time, start by asking him to turn the flashlight on, and if he has forgotten how, show him again. Keep working on that ONE thing until he is totally comfortable with it before moving on to something else. Keep reviewing the skills he learned earlier (by asking HIM to do it, not by "showing him" again), and eventually he'll master most of what he wants to do. I realize that you wanted a way to make teaching this stuff "quick and easy," but good teachers NEVER take the "quick and easy" path. You'll need patience and dedication. You'll need to go over the processes many times, and progress might be slow. But further down the line, you will be glad you were patient and understanding.

I resent the whole nature of this question and the answers! I know seniors who could run rings around you with technology. However, when ANYONE is learning a new device, it's easiest if there's an immediate need for one particular feature. What does he want to do with the phone? If he wants to take pictures, show him how to do that, how to upload them or post them. Let him do that for a while before you find the next thing he wants to do.