Hi Mark,
There are a couple of ways people can keep track of emergency contact information. The most common place to do it is probably in the communication values section of the persons individual view in Fellowship One. There is a communication value for "Emergency Phone", and you can even put a comment in so that you know who's phone number it is.
You can also use attributes, but you have less control over who has the ability to edit / attach attributes than you do communication values.
Blessings,
Jeff Lewis