From the 'Calls' or 'Contacts' tab (located at the bottom), select and hold the phone number/contact. If selecting from the 'Contacts' tab, select the contact name then select and hold the appropriate number.
Select the More icon (located on the right).
Select Add to Speed Dial (star icon located on the right).
Remove a speed dial
From the home screen, select Phone.
From the 'Calls' tab (located at the bottom), select and hold the existing speed dial entry (located at the top; above the 'All' and 'Missed' tabs).
Select Remove From Speed Dial (trashcan icon located in the lower-right).