The Ospreys are now short of cover in a pivotal position, with Phillips and Nutbrown joining Rhys Webb on the sidelines until at least the beginning of December.
Williams began his career as a scrum-half and was selected for the 2007 World Cup in that position so the move would not be entirely alien to the 2008 IRB World Player of the Year.
And with one of his regional coaches backing his ability to fulfill the role at professional level, Williams' potential switch could yet become a permanent one later in his career.
"Shane is a fantastic rugby player," said Ospreys coach Jonathan Humphreys.
"He has everything tailored to be a very good scrum-half.
"People have said in the past that that will be his position one day as the years creep on. And I think he sees that as possibly where he will end up.
"In terms of the injuries and where we are, it's a distinct possibility that Shane will start at nine for us this weekend."