Programmatically change phone numbers in Outlook

First of all, you need to allow Macro execution by going to Tools/Marcro/Security, then restart Outlook

Press Alt-F11 to open the Macro window. Below is the code skeleton for you to start with. 

Sub Outlook_Contact_Change()

    Dim folder As Outlook.folder
    Set folder = Session.PickFolder
    MsgBox folder.Name
   
    Dim contact As contactItem
    For Each contact In folder.items
        MsgBox contact.BusinessTelephoneNumber, , contact.LastNameAndFirstName
        ' contact.BusinessTelephoneNumber = "new number"
        ' contact.Save
    Next

End Sub