This article explains how to hide your phone number on an iPhone before calling someone.
Steps
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Step 1. Open the iPhone settings
This application is represented by a gray gear wheel and is located on the main screen.
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Step 2. Tap Phone
It is located in the middle of the menu.
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Step 3. Tap Show Caller ID
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Step 4. Turn off the Show Caller ID feature by sliding your finger across the screen
At this point, if you need to call someone, the call will be anonymous.