Problem: I need a way to quickly silence my phone and also return the sound to my phone.
Solution: There are two quick ways of doing this.
First, you could hold the power button. Under default settings, the phone will pop up an option, asking if you want to power off (the usual reason to use the power button), go to Silent mode, go to Vibration mode, go to Airplane mode, or disconnect/connect from/to the Mobile network. So if you choose Silent mode or Vibration mode, the sound will be off.
Second, there's an app for that. I use an app called "Volume Toggle(Free)". The app opens quickly and I can quickly choose from a lot of programmable volume schemes. By default they have Loud, Normal, Silent, and Vibrate. These are also editable.
I never seem to remember or have the patience for the power button method so I go straight to the app.