What could be the problem because my own voice is very weak when playback recording? Other's voice is recorder in good volume but my own doesn't.
Many phones have recording problems, especially when a bluetooth headset or a wired headset is connected. For most phones in the market Boldbeast Recorder can fix the problem perfectly if the user root the phone.
However your phone Xcover 3 uses the Marvell Armada PXA1908 chipset that is unpopular, so I'm afraid most developers include us don't know the chipset, even if you root the phone you are still hard to find a solution to fix it. Sorry for that.