"I had two major problem areas to cover and I knew I had to have more depth in midfield and defence than last season," the coach said.
"When Albert Riera was injured it left a gap in the midfield, and when the All Whites went on international duty there was little cover in defence.
"I had been on the lookout for someone who can play both in midfield and at centre back or full back.
"Roly fits the bill and will be pushing for a first team spot from the outset."
Bonevacia came to Merrick's notice through an agent and the coach was impressed when doing due diligence on the player.
"I watched eight or nine full games Roly played in and liked what I saw," Merrick said.
"He has an excellent background and I also spoke to the Roda coach that signed him.
"I talked to Roly and so did our captain Andrew Durante. We both felt he was the type of lad who would fit in at the Phoenix."
Merrick said he was also pleased that he was putting together a squad of young quality players.
"Roly is only 22 with experience behind him," he said.
"Alex Rodriguez is 20 and Nathan Burns 26 so our signings this season are bringing the average age of the squad down.
Bonevacia, his wife Milou and daughter Ivy-Mae will arrive in Wellington as soon as the relevant documentation is acquired.