Phoenix coach Herbert says Boxall will provide cover and competition for the established central defensive pairing of Andrew Durante and Ben Sigmund.
"Michael is a big, strong, quick defender who has impressed me when I've had him in All Whites squads," Herbert said.
"He's been playing in a good league and I'm confident he will be quickly up to speed with the A-League."
Boxall, 23, played his early football in New Zealand with Central United, Three Kings United and Ellerslie.
He went on to spend three years in the United States with the University of California Santa Barbara Gauchos.
He was selected first overall in the MLS supplemental draft by the Whitecaps last year, but after being part of the starting line-up early on, found himself on the sidelines.
"The football has been a bit disappointing in the last few months," Boxall said.
"I was out of favour with the coach and while I tried to do all the right things, it didn't make any difference."
Boxall made his New Zealand debut against China in March last year, and has made seven appearances for the All Whites.