The distance between the sensor and the lens needs to be the focal length to get a sharp picture if you focus on something that is far away from the camera. If you get closer to your subject the lens needs to be even a little further away from the sensor. So the lens needs some room to move.
A typical 1/3'' type phone sensor has a diagonal of ~ 6 mm. To get a typical wide angle shot the focal distance of the lens needs to be around 2/3 of the sensor diagonal, in this case roughly 4mm. So you need at least 4mm space between sensor and lens to focus at infinity (+ some 0.2mm for close up capability).
The only way to get around this problem would be a lower focal length for the lens. This would result in an even wider field of view on the same sensor size. To get the same field of view they would have to reduce sensor size. Smaller produce lower image quality (more noise, less dynamic range etc.)
Christian
Ok thanks. Just wondering what it was for.