R1 in the circuit is part of the input resistance to the op amp. The gain is -47/(10+2.2)
Draw the circuit out with the microphone amplifier FET having a grounded source, gate to the microphone element and drain to the coaxial cable center conductor. The equivalent output circuit of the FET is a current source. This in parallel with the 10k (the other end is to ground through the capacitor) is a norton equivalent circuit. Change this to a thevenin equivalent of a voltage source in series with the 10k and it will be more clear.
The gain of the entire two stages is something different. Try different values of the 10k and you will see that the gain is really the fet equivalent current source splitting between the 10k and the 2.2k and it is the current in the 2.2k that flows through the 47k to produce the op amp output signal. Making the 10k much higher will not raise the op amp output much. Making it smaller will decrease the op amp output because it diverts current away from the 2.2k.