Hi
I spent a good 30 mins searching for you on the net and was unable to find a (decent) phoenix and cross design.
However I would suggest checking out this site for the cross9es) inspiration
http://www.religioustattoos.net/Other_Tattoos/index.php
There are hundreds of phoenix designs on google images – take it to an artist who will put it together.
Once idea I had was to have a metallic phoenix wrapping around a cross made of nails.
Take care
Matthew