Hey @arrampico .
The connection a device makes is determined by the device and not the WiFi devices. Devices search for the strongest and/or most stable and uncontested channel and make that connection. Devices typically switch if there is a better or more stable connection on that same network but if it determines the current one is best it will stay on the currently connected one. The Google Wifi devices are providing the connection availability but not determining the connection made itself.
Please check your iPhone settings and/or contact Apple Support; there's likely a setting on the phone that needs to be changed.
