a crude simulation of a phone line transformer could be:

              220nF       ______
o---------o----||----o---|______|-----o-------->
          |          |     R 100      |
phone     |          |              .---'    To the Device
line     | |        | |               A
         | |        | |               |  5V Zenners
      R  | |     R  | |               V
     680  T     2k2  T              .---'
          |          |                |
o---------o----||----o----------------o-------->
              220nF