Wide angle lenses for system cameras (going back to the Contax and Leica of the 1930s) were often of retrofocus design, so that a very wide lens could mount on a flange of fixed distance from (then) the film plane. This became critical once SLRs were common -- you can make a 35 mm lens for a Contax or Leica rangefinder mount with a deeply protruding rear element group and still clear everything inside the camera, but once you have a moving reflex mirror between the flange and the focal plane shutter, you have a hard limit on how far the lens elements can protrude into the mirror box.

Now, fast forward 90 years -- even in 2022 almost no smart phones feature interchangeable lenses (two years ago, there'd have been no "almost" there), and they have software internal to the "camera" to correct for certain aberrations (like pincushion or barrel distortion), which can simplify the lens design -- especially for wide angle lenses. Rear elements can be as close to the sensor as they need to be -- so there's no need for all the extra elements needed just to make a lens mounted 41-45 mm from the sensor act like it has a 25 mm focal length.

Eliminating those requirements of system lenses (all of which are pretty recently descended from film camera system lenses) means the lens designs can be simplified which, in turn, lets a lens with the same focal length and aperture be physically smaller.