Summarize the following:
The Phone app typically has an icon that resembles an old phone.  Tap the app you use to place calls on your Android phone. It's the icon in the upper-right corner.  This opens the Menu.  Depending on the model of your Android smartphone, this may be an icon with three dots, three lines, or a button that says "More". It's at the bottom of the menu.  This opens the phone menu. It's near the bottom of the Settings menu.  Depending on the model of your Android phone, this may read "More Settings" or "Additional Settings".  On Samsung Galaxy phones, it's under "Supplementary Service." It's at the top of the More Settings menu.  Depending on your Android phone model, this may read as "Show Caller ID" or "Show My Caller ID." It's the second option in the "Show Caller ID" menu.  This hides your number when you place calls from your Android phone.

Summary:
Open the Phone app. Tap ⋮, ☰, or More. Tap Settings. Scroll down and tap More Settings, Additional Settings, or Supplementary Services. Tap Show Caller ID. Tap Hide Number.