I have two mobile phones.
My work iPhone is strictly controlled and managed. I could use it for personal use, but I find it good to be able to switch it off at the end of the day and have that separation from work.
The strict IT policies I work under mean there are limits on what I can install, and some functions limited.
My personal mobile is an account I had before I had the option for a work phone.
For a while I was able to claim my mobile cost as expenses, but eventually work policies made this untenable so I got a separate work mobile.
Carrying two mobiles can be a pain, but having that separation between work and personal life works well for me now.