Phal flower spikes very short

[opulenceflowers]

My Phal is starting to bloom which is still our winter in Cape Town. It is forming the flower spikes very short and some are bunching so much that there is not enough room for flowers to open. I do believe that the evenings are too cold in my greenhouse (around 13deg Celsius), but is this the only reason, or can it be lighting or too much feeeding (nit is half strength, but kept it up during winter) The greenhouse has a 70% shading all round and on top. I attach photo's. Second issue is that the plant is making very fat aerial roots - is this a sign of unhappiness?