The distance between the two cameras for stereo vision is on average the same distance as the human eyes = 63mm / 2.5inches. It also depends on the focal distance and the size of the captured subject. I want you to explore on your own the rig for the cameras / mobile phones and see what distance is the best for your intended use.
https://www.berezin.com/3d/tech/lens_separation_in_stereo_photog.htm
Stereoscopic Camera Rigs and Alignment
https://library.fiveable.me/advanced-cinematography/unit-9/stereoscopic-camera-rigs-alignment/study-guide/cmN4KsEvFbpkChgU
https://www.thoughtco.com/stereographs-and-stereoscopes-1773924
https://www.loc.gov/resource/stereo.1s42465
Library of Congress Examples
https://www.loc.gov/collections/stereograph-cards/
Stereoscopic Victorian Christmas GIFs
https://publicdomainreview.org/collection/stereoscopic-victorian-christmas-gifs/
Stereographic New York: animated 3D images from the 1850s to the 1930s
https://www.theguardian.com/cities/2016/feb/16/stereographic-new-york-animated-3d-images-1850s-1930s
FASHION STEREOSCOPIC GIFS
Red/Green Anaglyph glasses
STEREOSCOPIC GIFS
https://izismile.com/2010/05/07/cool_stereoscopic_animated_gifs_30_gifs.html
ASSIGNMENT
09 • Stereoscopic Imaging
Using two identical cameras, with a secure rig to protect them, and experimenting with variable lens distances, you will create two distinct sets of projects:
A) Static series of stereoscopic images > 3 still lives + 3 human portraits. Use Photoshop to emulate the look and style of victorian stereoscopic photos.
B) A stereoscopic video that will be seen using Red/Green Anaglyph glasses. The video must be 1080P, 24fps, recolored in Premiere/Avid/After Effects