In my experience, i had to water more freekvently than once a week when my phals are in plasticpots with slits. The medium does not seem to keep the moisture as long as in pots with dreinage only in the bottom.
But, as long as you have clear pots, its easier to judge wether you should water,slits or not.
As long as there is moist, i let it be. Mine is more often on the dry side, than the oposit...
Now in the summer, and the high tempratures now witch is unussual here, i have to water mutch more, some weeks up to three times, since the pot is all dry after two days, and i wait one more day, to bee on the safe side.
And im used to water about once a week... when our wheather is at its normal state.
I resently switch some of my phals into S/H, and this seems as an easier way to controll the watering, at least in my conditions. Im only on my first month, but this far it seems the phals has taken on to this as if nothing changed. They even seems to grow better roots now than before... I was skeptic, but stand corrected, about this kind of medium and growing.

At least this far...