It is not possible to completely disable voice control on an iPhone. If you have iOS 5 or higher, voice control is replaced by Siri, which it is possible to disable.
- Find your Settings icon
Press the Settings icon.
- Select General from the Settings menu
Find General on the Settings menu, and press the arrow next to it.
- Go to the Siri option
Scroll down the General Settings menu until you find Siri on the list.
- Slide the slider into the Off position
Next to the Siri option, slide the slider to the Off position. Once off, the slider changes from green to white.