I think the simple answer is to not look for a simple answer. After all, nature is never simple, and absolutes are rare.
The heroes were phased, but not "totally" phased. They were transparent to electromagnetic things (light, the solidity of objects) but not to gravity. And even then, they weren't totally transparent - they felt resistance, possibly in varying amounts depending on the solidity of the substance.
Diving behind a table is fine: the table is rock solid against the blast even if not against the hands of the heroes. Not going through the floors is fine: artificial gravity is acting on them since they don't float, and it must have a repelling quality even on non-phased objects, from the way we see it work.
The only real inconsistency is the availability of breathing air. But here I'd wish to speculate on what "phasing" really is. The word is used for describing at least four phenomena in Trek, after all:
1) The "ghosting" in this episode and in "The Pegasus"
2) The slight shifting in time in "Time's Arrow" et al.
3) The falling victim to a Starfleet hero's sidearm
4) The use of a transporter
For all we know, those all are one and the same phenomenon. The common end result is the making of the victim invisible (1, 2, 3, 4) and capable of going through walls (1, 4 but probably the others as well), after all! And "Time's Arrow" spells out what the phenomenon is: the victims exist slightly in the past or the future of the rest of the universe.
Enter Stephen King's Langoliers. If LaForge exists in the past of Picard (frantically handwave what this actually means if you really want to), of course light "remaining" of Picard will fall upon LaForge's VISOR, but light from LaForge won't reach Picard's eyes. And of course other things from Picard's timeframe will "remain" to seep into LaForge's realm, hopefully including sufficient breathing air.
This just makes one wonder: if you get phasered into oblivion, is that the very same thing that happened to LaForge and Ro? Is Trek Hell full of slowly asphyxiating and starving people who have no recourse other than to eat each other in the lucky case they were phasered down close to each other? Is it a merciful thing to phaser out your victim's heart or other innards, after all (TNG style), rather than to make him disappear in whole (TOS style)? (Is Hell covered in the innards of past victims?)
Timo Saloniemi