[saiya-jin]

Then I wouldn't call it personal phone, strange description from OP/quote. That term indicates to me a phone I own completely, hardware, software and all data like photos.

Same with laptops - if one decides to use work laptop for personal use its their choice at their own risk, but it doesn't become their personal laptop in any meaningful way. Even if hardware would stay after employment ends, every reasonable company would wipe it clean with some deep format & clean image of OS.