No, this still isn't in language I, or the field calculator, will understand. The field calculator works like: for each row in the attribute table, take some value(s) in another column(s), manipulate it somehow, and return some new value into the calculated column for that row.
Is "phw" the name of the column we are getting values from or calculating to? What does your notation phw[0,6.24] mean - something like if phw is between 0 and 6.24, apply this part of the formula?