There's something very ironic about the whole pass-your-hand-through-a-solid-object trope. As with TMP's "The Next Phase" and STARGATE SG-1's "phase out"/cloaking trope, one has to wonder: if this altered state makes you invisible and/or unreachable, or able to pass through solid objects, how come the ground/deck you stand on effectively stops you from drifting through the floor/ground?
Personally, I would say it's a matter of degrees for how much you're phased out of sync with normal matter. If the effect in "The Next Phase" had caused Ro and Geordi to fall through the floor, it's logical to assume they would have encountered other potential problems like not being able to breathe (the air particles would have passed through their phased lungs and not been retained for respiration). Since neither of those problems surfaced in their case, I think it's fair to assume (
) the effect wasn't quite that strong. We also saw it was relatively easy for them to be dephased even by Data's lowest wattage field, and they simply had to bump up the strength.
I don't watch Stargate, so I have no clue how they managed the effect.