Can the nursing home take my stuff?

My grandma is in a nursing home where my family and I were suspicious that she wasn't being treated with care. I put an old phone on voice record in her from after reading that this was the only legal way to do surveillance. I got my grandma's consent to record. Some workers found the phone and are now refusing to give it back. They're saying that they have to give it to their legal team or something. I feel as though if they didn't have something to hide, they wouldn't be doing what they’re doing. Can they do this? Can someone please fill me in on what is happening and how to resolve it?