The chip is slightly different for each application and is located on different boards in each system. The DXP plus has the chip on the CPU.
The CPU was labeled DXCPU-PLS-IC
The DXP has the chip on the services board.
The sevices board is labeled DXSRV-IC.
Later rev's are surface mounted and early rev's are plug-in. The FX was not yet released when I left Comdial. I have a supply of the chips. Thease were used because some guest computers had modems that would not work with the Comdial dialtone. That should not be a problem anymore with all the changes in PC's today