A bigger pixel count gives you a higher resolution image, which - all other things being equal - should lead to a better quality image. You'll be able to see finer detail as there are more blocks for the image to be broken down into. This will also allow you to print the image at a larger size without seeing the pixels.
However, with camera phones the limiting factors will probably be the quality (or otherwise) of the lens and the size of the sensor.
Once you reach the quality limits of the lens it won't matter whether the image is 30, 40 or 50 megapixels the image will look the same.
A smaller sensor will generate noisier images the the equivalent sensor on a DSLR. This will also limit (probably more so) the quality of the image.
Camera manufacturers have latched onto the raw megapixel number as an easy way of comparing cameras that looks like it should measure quality but it's not as simple as they are trying to make out.