The Phaser was probably not designed to enable repair, like most things. From the picture, it looks like there are two molded halves. If the glue they used to join those two halves, has not melted those pieces together, you may be ably to pry them open. But this can be a very risky process as this may crack the parts or at the very least, ruin the paint job.
You may have to make a decision whether to just have a display prop without working lights/sounds or risk opening up the two halves and possibly wrecking it. You may be able to put the cracked pieces back together, but it will, most likely, require filler, sanding and paint. It could be a very simple fix as to replacing a battery or resoldering a wire, but then again, the electronics could be unrepairable.
TazMan2000