This being said, the caveat is more sensor size than megapixels. Each pixel is actually a light gathering device with a micro lens above it, the more you have the smaller the lenses which results in less light being gathered and in turn equals more noise in the image. My 20.2mp full frame Canon which has a sensor the size of a 35mm negative, 36mm x 24mm, is just shy of the 25mp that is necessary for unlimited enlargement like film is capable of. Above that you aren't really gaining anything and are actually opening yourself to more image noise.
Phone sensors on the other end of the scale are far smaller, the biggest ever in a phone I believe was a 1/3" sensor at 4.8mm x 3.6mm! Now remember each pixel is a small lensed light gathering device, to add the 10 megapixels of a 2/3 sensor is like fitting the same amount into an area less than 1/3 the size!
What they do accomplish by going lower in the count is to increase the individual lens size thereby increasing native light gathering potential which gives them an edge in low light imaging without resorting to high ISO ratings which adds noise back into the image.