How do you make Billboard Guis enabled depending on Player's Backpacks?

Hey, people! I'm trying to make a Billboard Gui that becomes enabled if a certain tool named HackPhone is inside a Player's Backpack and un-enabled if it's not. The following Localscript is inside an Image Button inside the Billboard Gui. Can anyone tell me what the problem is? Thank you!

local Player = game.Players.LocalPlayer
while true do
    phone = Player.Backpack:FindFirstChild("HackPhone")
    if phone then
    script.Parent.Visible = true
    else
    script.Parent.Visible = false
    end
end