You cannot fully hide your phone number in WhatsApp
WhatsApp requires a phone number to create and use an account
You can reduce who sees your number by adjusting privacy settings
Open WhatsApp
Go to Settings
Tap Privacy
Set Last seen and online to My contacts or Nobody
Set Profile photo to My contacts or Nobody
Set About to My contacts or Nobody
Set Status to My contacts or My contacts except
Use a separate phone number if you do not want to share your main number
Avoid joining groups where unknown people can see your number
Block unwanted contacts if needed
Use WhatsApp Business only if you want a separate business number