Though phase sensors are standard what about giving them a detection range?
Depending on ship size they could detect phased ships at different ranges, since larger ships will have a more powerful sensor package. Off the top of my head, 100 for fighters, 500 for frigates, 750 for destroyers, 1000 for cruisers and maybe 1500 for capital ships and sensor stations. That's faithful to the lore since phase sensors are still standard on all ships but could still make them more useful and a lot trickier to fight when used cleverly.
Imagine, you can't detect any ships around a nav-buoy so send your hound over for a quick cap. Then out of nowhere a doom class that had been lurking outside detection range un-phases and suddenly you're down a frigate and there's a major threat moving in on your flank. I can imagine it making battles a lot more tense and exciting since it adds a lot of extra calculations that the player has to make about distributing his fleet on the map.
