Building a telephone spy
Image not posted as encouraging use is not considered wise technically or otherwise.

The device shown will land you in jail if used on a telephone system in most countries in the world. "Wire tapping" seems to be highly disliked by almost everyone. For private use the device may have its place but you probably want a more competent circuit.

This device is made to be line powered by inserting it IN a 2 wire  line by breaking the line. Cut both line wires, connect one pair to IN1, IN2, connect other pair to OUT1, OUT2. Polarity does not matter. Even IN and OUT are swappable. 

This device drops 2 x diode drops plus V = i_line x 200 ohms plus an unknown transmitter_on voltage drop across the bug. It would interfere with line operation in many cases (maybe all) and would be very detectable by any even vaguely competent detection system. It is possibly useful as a concept demonstrator but nothing more. 

Aerial, which you did not give an example of, can be a piece of wire. For maximum range there are special needs but this is so non ideal that it matters little.

If you REALLY want to tap a phone line with an RF bug that is line powered it should connect to the line with 2 wires, not break the line, run on the available 50V or 24V and pick audio off the two wire pair. You go to jail for using those also.