Coming back to the thread;
A few points that have raised themselves;
i) there should be some sort of specific dyslexia screening done in YR - this is a recurring theme that children with dyslexia and related educational needs are not being picked up quickly enough. Whether or not this test would do that, it should not be described as a 'test', and should be to screen, not to check up on teachers and pupils. I don't know if such a screening test exists, perhaps that is something that needs developing.
ii) children coming to school with speech and language delays and problems are not going to be helped by a 'phonics test'. And when there are significant numbers of children, either with speech & language problems, or with English as a foreign language, this sort of test can be very unhelpful. A friend of mine jacked in their job as a head, as he was utterly frustrated and depressed by the constant requirement to improve standards in the KS2 English Sats. His school demographic was a large number of Polish children arriving in Y5 or so, with no English. He pointed this out to the authorities, they said 'you must improve the number of children reaching level 4'. He said 'they don't speak English at all, 9 months before the SATS take place', they said 'you must improve the number of children reaching level 4'.
Not helpful really.
iii) of course teachers should be using the most effective methods to teach reading - the aim is to educate the children, not to pass tests though. I think a test administered at the point the child is deemed 'ready' would be good - with a maximum age cut-off - so a child who is doing well with their phonics could take it early, and if they got above a certain level, would not need to do it again (and presumably needn't waste time learning nonsense words in class, but could read a book instead). That would avoid the problem of able readers having to switch off their reading skills.