The Tykes have signed Phenix for a fee believed to be in the region of £25,000, with youngster Rhys Oates moving in the opposite direction on a one-month loan deal.
The 25-year-old told the club's official website: "My manager told me about the interest and it was a no-brainer.
"It all happened overnight. I just thought that I'd go for it and hopefully I can bring some success.
"I was used to training on Tuesday and Thursday nights. I'm looking forward to training every day and getting as fit as I can."
Before his departure, Phenix netted six goals in 14 appearances for the Conference Premier side.