Research has questioned the impact of synthetic phonics teaching, which was backed by a government literacy review.
Some say mixing phonics methods decreases its impact on learning
The government-commissioned research said synthetic phonics improved reading accuracy, but its effects on spelling and understanding were inconclusive.
The systematic use of phonics teaching should be in "a judicious balance" with other elements, the report said.
The government said synthetic phonics would be taught in England "within a broad and rich language curriculum".
'Fast and first'
The research, jointly carried out by the universities of York and Sheffield for the Department for Education and Skills, said evidence to support synthetic phonics over the analytic method was inconclusive.
"The review found no evidence for the superiority of either synthetic or analytic phonics instruction over the other," the report said.
One of the authors of the report, Dr Carole Torgerson from the University of York, said: "It could be the case that synthetic phonics is more effective, but we would like to see a large trial undertaken in the UK because the evidence base is very weak."
The researchers studied 12 randomised controlled trials to analyse reading accuracy, four trials to consider the effects on comprehension, and three to analyse spelling.
In December, former Ofsted director Jim Rose's review called for a greater use of synthetic phonics, saying it should be used "fast and first" in primary schools.
He said there was general agreement that phonic work is "essential though not sufficient" in learning to read.
Education Secretary Ruth Kelly said she accepted his recommendations.
Dr Torgerson said: "I am not saying Jim Rose is wrong, but in terms of the evidence base from randomised controlled trials we have concluded that we can't say which method we would recommend."
Debate has continued about the best way to teach phonics - which involves teaching the sounds of letters and their combinations rather than the letters of the alphabet.
Synthetic phonics teaches children to then blend those individual sounds together to form words, whereas analytic phonics teaches children how to work out the common sounds and letters in a group of words, e.g. push, park, pet, pen.
But the report acknowledged the positive impact of phonics on literacy: "Systematic phonics instruction within a broad literacy curriculum appears to have a greater impact on children's progress than whole language or whole word approaches."
Phonics should be a "routine part of every literacy teacher's repertoire and a routine part of literacy teaching", the report said.
A spokesperson for the Department for Education and Skills said the government backed the interim Rose report:
"This individual research report echoes the findings of Jim Rose's interim report, which makes clear that systematic teaching of phonics, set within a broad and rich language curriculum, is key," the spokesperson said.
Mr Rose's final review on phonics is expected early this year, and will inform the re-drafting of the government's literacy strategy, planned for 2007.