The more songs and the more photos you put on your phone, the heavier it gets. Only by a trillion-billionth of the tiniest fraction of an ounce, but still

The usual NAND-flash is filled with electrons in unused state and gets flushed when programming with a zero.

So your phone will geht lighter when you store something on it.

The more zeros, the lighter. So you better check the files you put on your phone on how many zero bits there are.

It's a bit more complicated with multi-level-cells, though.