finally it works:
set interfaces ge-2/0/15 unit 0 family ethernet-switching
set interfaces ge-2/0/15 unit 0 family ethernet-switching vlan members "v20-2nd-floor"
edit switch-options
set voip interface ge-2/0/15.0 vlan 80
set voip interface ge-2/0/15.0 forwarding-class ezqos-voice-fc
Thank You all for helping me !!!!! You are awesome.