The following mandatory TLVs are not configured by default in EXOS:    
 
- LLDP-MED Capabilities 
- LLDP-MED Network Policy 
- LLDP-MED Extended Power-Via-MDI TLV
   Use the following commands to configure them and allow the switch to communicate with the phone via LLDP:    
 
- enable lldp ports  
- configure lldp port  advertise vendor-specific med capabilities 
- configure lldp port  advertise vendor-specific dot1 vlan-name vlan  
- configure lldp port  advertise vendor-specific med power-via-mdi 
- configure lldp port  advertise vendor-specific med policy application voice vlan  dscp 46 
- Configure lldp port  advertise system-capabilities 
- Configure lldp port  advertise vendor-specific dot1 port-protocol-vlan-id vlan 
Above command would definitely resolve your issue.