Different model phones will have their buttons positioned differently, but the labels will be the same among brands.

Grandstream

(A) This is the phones PC port It can be used to let a device connect to the internet sharing the phone's connection. This does not need to be plugged in for the phone to work.
(B) This is the phone's LAN port. It needs to be plugged into a working network with internet access for the phone to work.
(C) This is the phone's power port. It is where you would plug in the phones power supply, but it is often not needed because the phone gets PoE from the internet port.
(D) This is a port where you can connect a phone headset. Call harbor doesn't offer headset for sale or rent, but you can buy and use your own.
(E) This is the handset port. On most phones, the handset will already be plugged into it.
Polycom

(A) This is the phone's power port. It is where you would plug in the phones power supply, but it is often not needed because the phone gets PoE from the internet port.
(B) This is a port where you can connect a phone headset. Call harbor doesn't offer headset for sale or rent, but you can buy and use your own.
(C) This is the phone's internet port. It needs to be plugged into a working network with internet access for the phone to work.
(D) This is the phones PC port It can be used to let a device connect to the internet sharing the phone's connection. This does not need to be plugged in for the phone to work.
(E) This is the handset port. On most phones, the handset will already be plugged into it.
(F) This port is the expansion port. It is used when attaching an expansion module to the phone.
Yealink

(A) This is the phones PC port It can be used to let a device connect to the internet sharing the phone's connection. This does not need to be plugged in for the phone to work.
(B) This is the phone's internet port. It needs to be plugged into a working network with internet access for the phone to work.
(C) This is the phone's power port. It is where you would plug in the phones power supply, but it is often not needed because the phone gets PoE from the internet port.
(D) This is a port where you can connect a phone headset. Call harbor doesn't offer headset for sale or rent, but you can buy and use your own.
(E) This is the handset port. On most phones, the handset will already be plugged into it.