How can I calculate the voltage over a microphone?
Page 1 hints at the value - it says output impedance is 2k2 and, given that the internal transistor is a JFET and, JFETs tend to have output impedances in the 10k+ range, it can be assumed that the 2k2 is the value of the resistor needed to power the circuit.

It'll be no problem with 2k2 but, don't forget to apply a very clean supply to the device - if you use 5V then filter it with a 1kohm and 10uF RC filter before connecting the mike via the 2k2.

Of note is the microphone current specified at a maximum value of 0.5mA - this is a guarantee that the microphone won't consume anything greater than 0.5 mA under quiescent conditions.