Do electret condenser microphones require phantom power?
Electrets don't need phantom power for the diaphragm, but the small capsules usually have a FET buffer inside which needs bias voltage. This can of course be derived from a phantom power source if necessary. 

Here is a typical electret circuit:



The value of the resistor is usually between 2k and 10k (cap say 10uF or higher) 
The datasheet for your capsule will probably give recommended operating conditions.

Here's a good link on simple electret circuits.
Another page with some more advanced ideas.