The versatile Australian signed for the club in 2012.
Vikings head coach Denis Betts hailed the player for his contribution.
“Cameron was a great addition to the Vikings squad when we signed him from Hull FC in 2012,” he said.
“He has been a key player for us in recent seasons and we are grateful for the contribution he has made to Widnes Vikings. We wish Cameron and his family all the very best for the future.”
Phelps himself was slghtly regretful that he was not staying at the club for longer.
“I just want to say a massive thank you from myself and my family to all the Widnes fans,” he said.
“I’ve really enjoyed my time at the Vikings and I’m disappointed that I couldn’t have stayed longer as I still feel I have a lot to offer.
“I’m going to miss all the lads. It has been an exciting four years and the progression we have made since rejoining Super League has been great.”