1. Connect a network cable to phone, if it doesn’t work, try the network cable in other network device. If other network device can’t get an IP address either please check the cable and your network environment.
2. If other network device can get an IP address, do a factory reset to the phone and check again. There may be a wrong configuration in the phone.
If phone still can’t get an IP address please try configuring a static IP address and check again (connect a PC to phone PC port then configure static IP address in phone and PC).
3. If you can access the phone by static IP address it should attribute to VLAN, please disable phone LLDP feature and check.
If the phone still can’t be accessed it should be a hardware problem. Please contact your vendor or local distributor and send the problem description for help.
4. If you can't get a help from them, please send an email which includes problem description, test result, your country, phone SN number to ticket.yealink.com