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