The Apple iPhone offers a Voice Control feature that is turned on by default. Use it to call one of your contacts or to speak a number to dial. Voice Control is activated by pressing and holding the "Home" button below the display until the Voice Control screen appears. Voice Control can be disabled only while the iPhone is in the locked mode to prevent voice dialing from a locked phone.
Turn on the iPhone. Tap on the "Settings" home screen.
Select "General" followed by "Passcode Lock."
Tap "Turn Passcode On" and enter or create a passcode when prompted. When the passcode is turned on, the Voice Dial feature can be turned off by tapping its "On/Off" switch on the Passcode Lock screen. While the iPhone is locked, no voice dialing can occur.
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If you do not lock your iPhone, you cannot disable Voice Dialing.