pfSense TFTP Issue

Hello all. I'm reaching out to see if anyone can help as I'm stuck.

I have inherited a small network in an office building which provides an internet connection for a Mitel PBX and a handful of Mitel VOIP phones. This network used to have a household Netgear router at its core and I have now upgraded to a Netgate SG-5100 running pfSense.

The issue I'm struggling with is that due to people working remotely we have the need for a few of these Mitel phones to work from the users' homes. This was functioning fine using the Netgear router configured by the previous IT admins but I'm having trouble with TFTP and pfSense.

I have gone as far as configuring a 1 to 1 NAT from a public IP to the PBX and allowing any and all traffic but the phones still fail to provision via TFTP. I have also enabled the "TFTP Proxy" available in pfSense on all cominations of the interfaces but I still cant get it to work.

If anyone has any ideas I would really appreciate the input.

Thanks.