Mullen, 27, joins the Phoenix on a one-year deal. 

The defender had previously been trialling at hometown club Adelaide United after leaving Newcastle Jets last season.

However, new Adelaide boss Marco Kurz elected to sign 23-year-old Jordan Elsey over Mullen. 

But the Phoenix were happy to pick him up instead, locking the one-time Australia international in for the next season. 

“When I left the Jets there was interest from a few different A-League clubs, as well as teams overseas, but either the club or the country wasn’t quite what I was looking for at this stage of my career,” Mullen said. 

“I spoke to Romeo Castelen who said only praise about [Phoenix coach] Darije [Kalezic] he told me he’s an excellent professional who will demand a lot of you, but is also a good football person, who will look to play a style of football that appeals to me.”

“I also knew about [Phoenix assistant Rado Vidosic's] reputation, so when the offer came it only took a matter of days. I’m grateful to the club, and I look forward to repaying that faith in me.”