Then you're required to sign a document acknowledging that when you leave the company they will remotely wipe your phone, including all of your personal apps, documents, photos, etc.
Mixing personal and work hardware is never a good idea.
I run into coworkers who then decide to use the company phone as their only phone, because the company phone is usually the top of the line iPhone or Samsung Galaxy replaced every 2 years when their personal phone otherwise is some mid range Android or 2+ year old iPhone.
Even when pointed out that the company can wipe it when they leave or even if they just suspect its been compromised, they don't seem to care. I just don't get it.
If someone intends to leave, they can first revoke the company's access to their phone.
If the company has the software installed to remote wipe a phone, they have the software to stop you from locking them out.
Maybe their lives are just not tethered to their phones. I use my phone for phone calls, texting, and maps/navigation. That's about it. It would be a bit inconvenient to lose my contact list without warning, but I export those periodically in case I lose my phone.