Try this...
  Dim a, b As String
  a = TextBox1.Text
  b = (TextBox2.Text)
  Select Case a
    Case "Julius B. Tanguilig":
      TextBox2.Text = "09268862690/425673"
    Case "Jodel D. Avendano":
      TextBox2.Text = "09053146571/432467"
    Case "Mara Grantoza":
      TextBox2.Text = "09357648907/423094"
    Case Else:
      TextBox2.Text = String.Empty
  End Select