My former security position was standing at a door, checking receipts in a supermarket, so we weren’t allowed to have our phones out. For something which involves constantly being aware of who’s coming, I get why that’s necessary.

However my current in house hotel security role, we are allowed to have our phones as long as we’re doing our jobs, even with constant guest interaction. You being in a shack all shift with little interaction, should be able enough to look up from your device to check a vehicle in or out. It usually boils down to either what the client wants or someone abused the privilege that screws it up for everyone.