Hi, Martine. In my personal experience, good light (often more than you would think) is the secret to getting spikes. I was able to increase the light for my phals in April by putting them outside on carts on sunny days and rolling them back in a night, and they have set 17 new spikes since 4/1-- nearly every phal not already in bloom that is big enough to spike. Most but not all were from phals with a high % of summer bloomers in their ancestry.
A 50% increase in light is often recommended by specialists for inducing spikes on phals, see culture notes at Bedford Orchids, Robert Beddard Nurseries and Big Leaf Orchids. These are all excellent notes, written by distinguished phal breeder/growers for new growers. A few minutes reading them will repay you handsomely in better growth and blooms on your phals. And yes, they all recommend increasing light.
url to Big Leaf notes on growing and blooming phals, for new indoor growers.
Big Leaf Orchids -Information
Good luck.