I am not sure what you mean by each lens, since there is only one lens with this technology. The diameter of the lens has to be comparable to the separation between the two lenses in a stereo system. For meaningful stereo effect at distances we would find interesting (say, a few feet between you and your toddler), this has to be maybe an inch; I don't see a smaller lens being very interesting.
For a typical cell phone, the hyperfocal distance - beyond which everything is in focus with the lens focused at infinity - is maybe 6 feet; you can't get light field information, at all, for anything further than that. And it will be only a tiny bit of information for closer subjects; you can't take shallow depth-of-focus photos with a cell phone, and you can't apply this technology for the same reason. BTW, motion blur is likely a bigger problem for cell phone photos than focus.
For a typical cell phone, the hyperfocal distance - beyond which everything is in focus with the lens focused at infinity - is maybe 6 feet; you can't get light field information, at all, for anything further than that. And it will be only a tiny bit of information for closer subjects; you can't take shallow depth-of-focus photos with a cell phone, and you can't apply this technology for the same reason. BTW, motion blur is likely a bigger problem for cell phone photos than focus.