Which DISPLAY variable for Phindows?

Hello,

We would like to run X11 applications like emacs via
Phindows. Our problem is that emacs gets launched
on the attached screen of the QNX node, not in the Phindows
session. The DISPLAY variable is currently: 127.1:0.
So this is actually not a surprise. The question is,
what DISPLAY variable do we have to set for the Phindows
session? How can we find out?

(We have installed QNX6.2.1a, the XFree binaries and
libraries and XPhoton)

Thank you all

Dorothea