The former Wigan centre was released by Wigan last season, and was free to play for the Arlie Birds in March after his visa cleared.
Hull FC released the 26-year old at the end of last season, having played 19 games and scoring only two tries during his time at the KC Stadium.
Phelps played for Canterbury Bulldogs in the NRL before coming across to join the Warriors. He was highly rated having made his debut for the NRL Premiers in 2005, a year after the Bulldogs won the Grand Final.
Phelps is expected to be given either the number 18 or 19 squad number by his new club, after coach Denis Betts omitted the two number from his official squad announcement.
The Vikings are also expected to announce the signing of an NRL player soon.