The iPhone’s default behavior selects screen options by single-tapping them, but the VoiceOver feature overrides this behavior. With this accessibility option enabled, single-tapping makes the iPhone audibly read a selected menu item, so you can interact with the device without viewing the screen. To select an option when the VoiceOver option is enabled, you double-tap it. To restore single-tap selections, you disable the VoiceOver feature. Warnings Writer Bio

How Can I Turn Off the Double Tap From My iPhone  - 96