Well, i think Phex is (at least a little) safer then Limewire/Frostwire, because i get ALOT LESS fake search-results when i'm using Phex.
My PC is online 24/7, my Phex is running 24/7 too... i have a (forced) Ultrapeer status, and when i search for something i get almost NO fake-results!
When "safe" means LESS FAKE search-results, then i say: Yes, Phex is more safe then Limewire/Frostwire!
But my Phex is a Ultrapeer, so maybe that makes the difference?
I would say: try it yourself