I believe safety incorporates phast within it, but uses the results to generate QRA type numbers ( risk contours etc)
Phast is specifically a dispersion tool / flame distance / explosion simulation , the results of which used to be incorporated into a QRA in a more manual way.
but depends on what you want - you need to ask DNV GL
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
