I suspect the default focal distance for smartphone cameras is a bit too wide-angle. I haven't tried recently, but zooming in a bit (say 1/4 to 1/3) would help,

I suspect the default focal distance for smartphone cameras is a bit too wide-angle. I haven't tried recently, but zooming in a bit (say 1/4 to 1/3) would help, as would tracking the target (panning slightly so the main subject stays in the center). It all really depends on how close the subject is. You need to exaggerate the separation a little but not too much. In an airplane, the time between shots (and speed of course) determines the separation. If you're doing the same thing on the ground, it depends in how far your subject is, but you can step 1-2 feet sideways for your second shot. You just have to experiment to find what works. I have tried on an iPhone before, but the default "slide" between photos isn't fast enough to get the effect, so I had to download them to my PC. Maybe there's an iOS app for it now. Edited to add: I knew someone in the age of film who screwed 2 SLRs to a piece of wood about 16 inches apart, for 3d landscape photography. He used 2 mechanical remote shutter releases to make sure the photos were in sync. A similar rig with DLSRs and electronic remotes should be easy and more precise (to get same settings and synchronous release). I'm surprised I haven't seen it done yet.