Turntables (phonographs) need a special boost and EQ compensation to work with mixers, unless you are using a DJ mixer. DJ mixers include what are called called phono preamps. The XENYX mixers do not come with phono preamps.
The solution is a PP400. Simply connect your turntable output to the INPUT of a PP400, then connect the OUTPUTS of the PP400 to INPUTS on your mixer.
You can see a PP400 at: