If you just echo the php code, it won't be parsed by the php parser and actually executed.
So if you did something like:
echo "phpInfo()";
PHP would simply write "phpInfo()" out to the browser, and not actually execute the funciton.
On the other hand, if you did:
eval ("phpInfo()");
That will actually execute the function there.
So what you'll want to do is something like:
eval($row["phpCode"]);
Hope that helps!