A few months ago I repotted some phals in expanded clay 8mm-10mm
granules and they have been loving it (new leaves, new spikes, new
roots). Granted I had to modify the watering somewhat (slightly more
often) but I am extremely pleased with the results so far. Next ones I
repot will probably be a bark/leca (30/7) mix however to maintain the
humidity for a little longer. LECA is fantastic for air flow through
the roots and I think aesthetically it's very pleasing too.