Yup. Anything metal messes with GPS. Phones have fallback modes but they can fail spectacularly at times. Even outdoors--sometimes my phone won't navigate sitting on the passenger seat (The GPS constellation guarantees a minimum of 4 satellites above the horizon, it doesn't guarantee 4 satellites in positions that won't be blocked by your car roof.) If you drive onto the property with your phone on your person or in a purse on the passenger seat the geofence might fail to detect it.

There's a boss somewhere who didn't look into this well enough.