Sniff... Sniff... I caught a whiff of homework...

It appears that you're being a tad too lienient with your users by allowing them to enter a phone number in any way they please. Provide some guidance to your users!! That is to say, provide a separate <input> tag for each element you want to capture and validate:

<b>Please enter your phone number:<b>
<table border="1">
<tr>
<th>Area Code</th>
<th>Phone Number</th>
</tr>
<tr>
<td>(<input type="text" name="area_code" size="3" maxlength="3">)
</td>
<td>
<input type="text" name="phone_exchange" size="3" maxlength="3">
-<input type="text" name="phone_number" size="4" maxlength="4">
</td>
</tr>
</table>
[download]

So, you've decreased the complexity of your validation routine at the cost of a few more fields and the tiniest bit of pain for your users.

area code: /^\d{3}$/

phone exchange: /^\d{3}$/

phone number: /^\d{4}$/

HTH.

C²