Place this code In the sheet code module you wish To use it on: 
 
Option Explicit 
Dim rTargetCell As Range 
Private Sub Worksheet_Change(ByVal Target As Excel.Range) 
    With Target 
        If .HasFormula Then Exit Sub 'If a formula is entered
        If .Column <> 9 Then Exit Sub 'Column 9 = I (won't run if not this column)
        If IsEmpty(Target) Then Exit Sub 'If the range gets cleared
    End With 
     
     
     ' Assign the target cell to a module wide object variable
    Set rTargetCell = Target 
     
     
     'If a number is entered, run the macro Excuses
    If IsNumeric(Target) Then 
        Excuses 
    End If 
     
     'Explicitly clear memory
    Set rTargetCell = Nothing 
End Sub 
 
Private Sub Excuses() 
    Application.EnableEvents = False 
     'Check what was entered into the target cell
    Select Case rTargetCell.Value 
         'If a 1 is entered, put "Reason 1" in the cell
         'You can change the text between the quotations
    Case Is = 1 
        rTargetCell.Value = "Reason 1" 
         'Same as above for the number 2
    Case Is = 2 
        rTargetCell.Value = "Reason 2" 
         
         'enter as many cases as required
         'If a number not listed above is entered default to this message.
    Case Else 
        rTargetCell.Value = "Please call us for further explanation" 
    End Select 
    Application.EnableEvents = True 
End Sub