Pixel: –Pixel(in camera) is the tiny photo sites or light receptor of a camera sensor. It collects the light coming from a source.
Pixel Quantity: It is the quantity of tiny light receptor in an image sensor.
If it says the camera is 1 MP (Mega pixel) then the total pixel of the sensor will be 1 million.Higher the pixel in number larger will be the image size.
In a phone camera the sensor is small (and thus pixels are also small) . For such a small sensor, area for the high number of pixels are very less and thus the higher number of pixels makes the density higher and for which the required light cannot capture properly by the pixel. So phone camera even with higher pixel cannot make a good quality image like other camera does
Only the higher pixel doesn’t make an image good in quality. The quality depends on other factor also, like the pixel size, light,sensor size, the lens quality use by camera etc