You cannot fully hide your phone number in WhatsApp
WhatsApp requires a phone number to create and use an account
You can hide your number from people who do not already have it by adjusting your 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 except or My contacts
Turn off Read receipts if needed
Use a separate phone number if you want to keep your personal number private
Use a business number or secondary SIM for WhatsApp
Avoid sharing your WhatsApp link publicly if you want less exposure
Block contacts you do not want to see your profile or message you
Use WhatsApp groups carefully since members may see your number depending on group settings
Check who can add you to groups in Privacy settings
If you want stronger privacy, use a different number dedicated only to WhatsApp