TV3NZ have confirmed the story is true. They are running two seperate articles on it.
https://www.newshub.co.nz/home/sport/2018/05/footba...
Wellington Phoenix confirm merger talks for partnership
The article is titled "Wellington Phoenix confirm merger talks", but the third paragraph states "It (the Phoenix) didn't deny it had been involved in reported merger proposal talks with a consortium from southwestern Sydney" which to my way of thinking is certainly not the same as confirmation. The rest of the article is just a cut and paste job of what is being reported in the Australian media (xyz reported . . .) and the Phoenix's statement - there is no new information there.
The Siggy article is titled "Phoenix legend Ben Sigmund laments reported merger" and in the article "the suggestion his old outfit might be shifting across the ditch".
These articles are certainly not stating that the story is true, they are commenting on the story.
The first three paragraph read like they confirmed the story to me, if you read it differently so be it.
The Wellington Phoenix say they are in discussion with potential club partners, but have reaffirmed their A-League licence is not for sale.
In a written statement, the struggling club admitted it was talking to "parties interested in participating in the expansion of the A-League".
It didn't deny it had been involved in reported merger proposal talks with a consortium from southwestern Sydney.