The Bayonne number nine has struggled for consistency in recent months, but Howley believes that Phillips can return to his previous level of form.
"Mike is back playing to some level - he needs to get to the next level, to where he was. He has gone away to France, and I have tried to give him some stats in terms of the brand and type of rugby they are playing," Howley told reporters.
"When he plays for us, he makes 60 or 70 passes a game. In France, it's 20-25, so that puts pressure on his conditioning. Mike has been told. On his day, when he is fit and confident, Mike is probably one of the best number nines in the Northern Hemisphere. We need to get Mike back to his best.
"He has got pressure with Tavis Knoyle and Lloyd Williams, but you would like to think, if Mike is back to his best, he's got a huge part to play in our performances in the Six Nations."
Wales open their Six Nations campaign against Ireland on February 2.