I think that depends on what your goals were for starting phonics, and how your child is doing with reading and spelling.
For example if your child is reading and spelling well, and simply needs fluency practice, I feel it is ok to stop phonics, and continue with other spelling instruction.
Another example is if your goal for phonics was simply to get the child started with reading, and they caught on quickly, then I say it is ok to stop.
If your child has dyslexia and is struggling to read, you may want years of intense phonics.
We have experienced both sides of this. Reading Reflex is my current favorite, and one child flew through it in months, while another had years of intense phonics.