You can read this page of Bernard Lagrelle Site : Phalaenopsis mannii. Look at the bottom charts for temperature and rain during winter months.
My mannii becomes huge and this is one the few Phals that I grow in the GH to give it low night temp. in winter (13-15°C at night), I water it once a week (it's a mounted plant) but the hygrometry is high in the GH. It blooms each year easily in April/May.
This is only "my" experience.