Despite also boasting a 100 per cent record, England have yet to hit top gear labouring to victory in Edinburgh and Rome but Phillips believes that could be all the motivation they need in front of an 82,000 sell-out crowd.
"It is going to be a difficult game," said Phillips. "They have won two games, and people haven't been giving them much credit. We know they will be going out to prove people wrong.
"England might say themselves they haven't fired or clicked yet, but they are only one game away from possibly doing that. They have got some great players and they are a major threat.
"People are quick to criticise, but I think it has been harsh. They have had two good wins on the road, so they must have good belief and confidence in themselves.
"They are going to be firing - it's going to be a proper Test match."
Phillips was the catalyst for Wales' last Grand Slam season in 2008 when he scored the winning try at Twickenham in an extraordinary 26-19 win, their only victory at the home of English rugby since 1988.
The 62-times capped Bayonne star believes Wales are well-stocked to repeat the feat in their quest for another clean sweep but insists there is still room for improvement.
"The good thing about this Wales team is that there are so many threats in the side. We are playing some good stuff, but, at the same time, I think we have left a lot of points out there so far.
"We can be confident from our last couple of performances, but we know we need to improve."