If we configured your phone system, your Voice over IP (VoIP) phones can share an Ethernet port with other devices at your workstation. Likely you are already sharing your Desktop computer and your phone this way using a single.
What if you want add more devices, like a workgroup printer with an Ethernet connection? To do this you will have to get a small unmanaged switch, like one from Netgear, Cisco or others.
The key is that the phone's network connection be plugged directly into wall jack. Then you can attach the unmanaged switch to the "Desktop" port of the phone, and your other appliances, like your Desktop computer, will also be connected to the switch.
The unmanaged switch should never be "upstream" from the phone, i.e., between the phone and the wall jack.