Can the PHONE-DEX be used with an office line?
If the office telephone line is digital, then a converter may be needed, such as the Konexx Konference. Set it up by plugging one end of the converter into the PHONE-DEX and the other end into the socket on the office phone where the handset usually goes.  Next, plug in the power cord. There may be static when trying it for the first time.  If this is the case, move the switch numbered 1-4 to improve the signal.