sudo requires root password
If your user is an admin, they should (by default) be able to use sudo (based on the contents of the sudoers file).

If you re-enable the root user, and examine the contents of the file at /etc/sudoers, you should find this line (which specifies that the admin group has the ability to use sudo):

%admin  ALL=(ALL) ALL


It may be a good idea to confirm that "phil" is in the admin users group. You can perfom this check on the command line using this command (after you've re-enabled root, of course):

sudo dseditgroup -o checkmember -m phil admin


It's also possible that the rootpw flag may be set in the /etc/sudoers file (this should be off by default). If you find the following line in that file, see if deleting it will help:

Defaults rootpw