Is it possible to configure a work iPhone to have the company user and the personal user separated? I have a company's iphone, and I would like to use it for personal purposes, as well as a testing device. 
The problem is that this is the only test device of the company, and since I'm allowed to use it with my personal phone number and data, the problem is that any day, somebody can request the phone to use it for test something (it's very improbable but posible)
For this reason, I would like to know if it's posible to "lock" my personal user/data and/or switch to another user (the company's user) in a safe way so I can share the phone without having to be worried about somebody else seeing my what's app push notifications, my personal camera roll, etc...
No, that is not possible with iPhones.

Your only option is to take an encrypted backup and deleting everything on the iPhone before giving it out to another user, and then restoring your backup when you get it back.