Controlling volume on iPhone has been pretty straightforward since the first model. You have three volume buttons on the left side. The Mute switch ... there’s the slider in Control Center ...

you’ll have to change a setting to bring the volume slider back to your iPhone’s Lock Screen — here’s how. Open the Settings app. Select Accessibility. Select Audio and Visual. Toggle on the “Always ...

play some music (or any other type of audio) and lock your iPhone. When you turn the display on, you'll see the same playback control widget as always, but this time, it will have a volume slider ...