Is it illegal for a company to take and hold a cell phone for 3 days?

here is the situation. i work for a rather large company and they caught one of the employees with a cell in her pocket. the company said they wanted to confiscate the phone until monday. she is without her phone until then. i have stated to said company they are depriving her of her personal property and they can be arrested for it. now i wanted to ask this before i advised her to call the cops and report it stolen by the company and the company refusing to give it back at the end of her shift. if you have some advise then let me know what to tell her