I'm not sure how these subpoenas usually are worded specifically, but it doesn't seem like that contrived of a situation. Like, if you aren't the suspect and are ordered to hand over all devices used to communicate to <suspicious co-worker X>, if you have a separate device you just hand the thing over. If you hand over a personal phone, they are presumably going to bump into your walled off section and have some questions. Plus, you don't have a phone, while they are working on the thing, which seems like a pain.

This is assuming you aren't in a "hand over all electronic devices" kind of situation.