How to populate Word userform textbox with results from Combobox If statement results

If you are listing known names I would probably use a list box rather than a combo box, but nevertheless you need something like

Private Sub UserForm_Initialize()
With Me.cmbPMname
    .AddItem "John Brown"
    .AddItem "Fred Smith"
    .AddItem "Bill Jones"
    .ListIndex = 0
End With
End Sub

to populate the box and select the first item which will show the associated phone number of that first item in the text box. To account for alternative selections you then need to define the text box values associated with the names

Private Sub cmbPMname_Change()
Select Case cmbPMname.Value
    Case Is = "John Brown": txtPMphone.Value = "(810) 766-07659"
    Case Is = "Fred Smith": txtPMphone.Value = "(810) 785-12345"
    Case Is = "Bill Jones": txtPMphone.Value = "(810) 901-76543"
    Case Else: txtPMphone.Value = "No phone listed"
End Select
End Sub

The Case Else statement allows for the fact that you are using a combo box and the user may enter some name that is not associated with a phone number. The user would still be able to over-write the value in the text box if the text box is editable.