The Plantronics U10 cord, also known as the 26716-01 cord is a commonly used cable that has different ways in which it can be used. The U10 cable can plug into a Plantronics amplifier such as the M12 or M22 which then allows a Plantronics H series headset to connect in via the Quick Disconnect (QD).
The amplifier then connects to the host phone allowing the headset to then be used. If the phone is compatible, you can plug the U10 cable directly into the headset port on the phone and the H series headset into the cable. This eliminates the need for the amplifier base, but you'll want to double check that your phone allows this 26716-01 cable to be used.
Different direct connect cables exist so you'll want to make sure that your phone accepts this specific one. One advantage of connecting directly to the phone is less clutter on the desk making for a cleaner, more clutter free work area. The U10 cord is coiled which allows it to expand to almost 10 feet when fully flat giving you a lot of cable length to move around your immediate work area.