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Let's take, for example, the Moment Tele Lens. This lens is pitched as a 60mm lens that allows you to get 2x "closer" to the subject.
The iPhone 6s uses a f/2.2 lens.
Does the mounting of the tele lens onto the iPhone change any characteristic that would affect the ability to produce bokeh? If so, how?
Yes and No.
The FL of a lens has a significant impact on the DOF, what is not in focus, and how it is rendered.
This is a 2x adaptor which makes the FL twice as long and the FOV 1/2 as wide. For any subject distance and aperture setting a lens that is twice the focal length will have approximately one quarter the DOF of the shorter lens. There will also be a loss of exposure due to spreading the light over a larger area (magnification) equivalent to doubling the aperture to f/4.4. However, I'm not sure if this type of adaptor will cause that to also affect the DOF the way a 2x teleconverter does for a DSLR lens... if it does, the net reduction in DOF is approximately 1/4 (2x focal length and aperture #) for any given subject distance.
Additionally, the narrower FOV and greater magnification will impact the size at which BG elements are rendered (amount of blur/bokeh characteristics). This can range from negligible if the BG is very close behind the subject, to very significant if there is a lot of BG separation (it can result in an entirely different image overall).
The "no" part is due to the fact that it is for use on a very tiny cell phone sensor. So even though it will have less DOF, it will still probably be quite a lot... the difference may not be evident in many/most situations (most evident for very near subjects).
