Most parents do not need to be convinced that phonics is a very important set of skills for any reader to master.  What often makes teaching phonics so challenging is understanding, and keeping track of all the different skills you are supposed to teach.
There are the digraphs and dipthongs and consonant blends and silent 'e' and so on.  It all seems to run together, and if your child seems to be struggling in his efforts to decode, how do you know what particular skill is weak? The phonics test developed by the reading specialists at The Struggling Reader is designed to bring clarity to the phonics question by addressing each of the major phonics components a developing reader needs to master.  Rather than getting a general score that suggests you need to work on phonics, you will come away with a clear idea of the specific skills that need to be addressed.
After much field-testing with parents just like you, the format consists of a series of index-sized cards that are shown to the student, one after the other.  A user-friendly scoring guide accompanies the cards, and allows you to note the particular types of errors being made.