Regular Expression For US Phone Numbers?

Here is the form in question: spraytechDOTcom/download_form.asp I am so close to getting this to work the way that I want, but here is what I am having an issue with: I cannot seem to make it look for the 12 digits that are in the phone numbers that we are going to collect. Ex. 800-123-4567

It doesn't have require 12 characters if there is another way to get the number to validate looking like the example above. Here is my regular expression that I am struggling with:

var re = /[^d-]$/ It seems to block any letters, but it will accept only 1 number. I would really like it to make sure that the phone number is only entered like this: 800-123-4567.

I have looked for days trying to figure this out and have only gotten close.