Open WhatsApp
Tap the chat with the person
Tap the contact name at the top
View the phone number in the contact info
If the number is not saved, open the chat header to see the number
Tap the profile photo or name to open details
Check the About or Info section if needed
Use the search bar to find the contact by name if saved
Open the contact card from the chat to see the number
If the number is in a group, tap the group name and select the participant to view the number