Is the work's Polycom VOIP phone able to contact the VOIP servers ? ( i.e. not being blocked by VM Child Safe which are controlled in the VM online account )
I wonder if you can see ( or ask about ) the SIP port settings on the VOIP phone from your employer.
Hub / Router SIP ALG appears to be a problem for VOIP kit that uses the standard 5060/61 (TCP/UDP) ports for traffic inbound to the phone.
Our VOIP provider is Sipgate and specifically to overcome SIP ALG issues of domestic broadband routers a wide range of non standard UDP port numbers are supported. Our Cisco VOIP kit has 2 lines working fine using a set of RTP & UDP ports in the 46xxxx range.
The VM Residential Hub(3/4/5) support a telephone service in both Router vs Modem mode, so the SIP ALG status might not change with Hub mode. I'd be super happy to hear otherwise on that if the actual situation differs.