Phantom power on the S16 Snake can be controlled from the X32 Desk. Some things to check if it is not working:

There are a couple of settings that could keep you from turning on 48v from the console, and they're all found under the Preamps tab under Setup. On the far right side, you want to make sure that HA Gain Split, Lock Stagebox, and the 2 HA remote boxes are all unchecked. Any of these would prevent phantom from turning on.