PHx is for Evolution.
Luckily, we have it built in with Revolution!
They are called Output Modifiers, and their docs can be found here:
http://rtfm.modx.com/display/revolution20/Input+and+Output+Filters+(Output+Modifiers)
The "notags" phx has been ported to an output modifier, and uses the same name. Just slightly different syntax.
Another thing I notice, you are using this for your GUID:
<guid>http://www.fruitflylife.com/?id=[[+id]]</guid>
While it works, it’s maybe better to use a link tag. Basicly:
[[~1]] becomes index.php?id=1
[[~1? &scheme=`full`]] becomes http://www.fruitflylife.com/index.php?id=1
[[~[[+id]]]] generates a relative url to the resource with the ID as passed in the [[+id]] placeholder
[[~[[+id]]? &scheme=`full`]] becomes an absolute url with your site url (http://www.fruitflylife.com/) in front of it, to the resource with the ID as passed in the [[+id]] placeholder
If you use the link tag, you have the extra benefit that if you were to start using friendly urls (eg
http://www.fruitflylife.com/upcoming-events.html) the link tag will start using that instead of index.php?id=N. If you change the alias the link tag will update etc.
Hope this helps!