IMHO you can't set levels or goals in syntaxical terms.
I think styles, methodology, stability, optimization, crossplatforms and all the other stuff I can't be arsed to list are more important.
Also you have your various segments of php which would need to be covered under any "level" scheme.
e.g. filehandling, arrays, classes, mysql, pgsql,sessionhandling blah blah blah..
Even down to if you use <PHP>" "*4</PHP> or <PHP>\t</PHP> for indentation.
Its something which cannot be defined through levels.
