"Option 128 missing" tells me that while the new phone is getting a DHCP offer, it doesn't contain settings that the set recognizes as valid for a Mitel IP phone. So either there's a teleworker involved or the new phone is unable to get onto the correct VLAN, possibly due to L2 switch port configuration issues.
Check the static settings on one of the working phones, particularly look for ICP addresses and VLAN assignments. Also check the L2 switch config, just to be sure the switchport isn't set up for a different VLAN or something. You could even try plugging the new phone into the same switch port as one of the working phones and see if it comes up there. If all else fails, enable the PC port mirroring on the phone and do a Wireshark capture of the boot sequence of both a working phone and the new phone, and compare what looks different.