Open the Phone app
Tap Contacts
Find and open the contact you want to delete
Tap Edit
Scroll down and tap Delete Contact
Tap Delete Contact again to confirm
To delete multiple numbers, open each contact and repeat the steps
To remove a recent call, open Phone
Tap Recents
Swipe left on the number
Tap Delete
To delete all call history, open Phone
Tap Recents
Tap Edit
Tap Clear
Tap Clear All Recents