I have a Samsung Galaxy S8. When I delete a phone number from a contact, it seems to take effect, but when I check the contact again, the number is still there. Details as follows: Select Contacts. Select an entry (in this case, my Dad). There are two "Home" numbers listed; the old and the new (entered about a week ago). Press Edit. Under "Phone", press the "-" symbol next to the desired number. It is removed from the list. Press Save. When the contact details are displayed again, the deleted number is still there. I've googled and several response say to either clear the specific Samsung app (don't know which one) or to clear system cache. I have not cleared the system cache yet - waiting to see if there's another solution.