There’s a vast spectrum covered by the concept of “two phones, one person.”
In general, it’s a bad idea to use your own phone for your job — for all the same reasons why it’s a bad idea to use your own PC for your job. If all you use your phone for on the job is phone calls and SMS, it’s probably not a problem. But as soon as you start down the road of company-controlled messaging systems, two-factor authentication … and, especially, using the camera, storing documents on your phone, and the rest … well, you’re opening up everybody for a world of hurt.
Any company that has any sort of security standard it must adhere to (HIPPA, financial, etc.) will forbid you from using your own devices for work. That, or they’ll essentially take ownership of your computer, forcing you to install their own spyware and the like. (Don’t let them! Make them provide you with company-owned devices. If you have no other choice, buy your own dedicated stand-alone devices that you only use for work. Another option: have the company provide you a dedicated VM that they host, and never do anything other than remote into it.)
Another not-unusual scenario is that of the developer who needs to make things that run (and run well) on multiple platforms. Closely related are product reviewers.
Past those sorts of scenarios, there’s less and less reason for multiple phones. But, “because I want it,” provided you have the means, is, of course, a perfectly valid reason.
Cheers,
b&