... the company servers if you give a shit about security.
The whole BYOD argument has been debated to death. Point is there are two camps here.
Camp 1 says "No, because security" and Camp 2 says "Yes, because I'm lazy and like my toys."
Hmmm no bias detected in that statement... though you did openly admit that you're a camp 1 member later on. I will tell you right now that I've worked for several companies with people like you calling the security shots. I can also tell you right now that I will never carry a company phone, no matter what my boss wants. Most engineers I know have zero interest in a company phone. The only people I know who do want one are managers and sales types. If you want somebody outside of those two groups to be connected, you have to allow BYOD to some extent. You may not like it, and you may think its all about the toys, but that's just because you're way too uptight and don't realize that people want a work life balance. Carrying a corporate phone is like having an electronic leash around your neck.
You can have all the security in the world if you disconnect your network from everyone else. No one will be able to get anything meaningful done. You have to balance the needs of your employees with the needs of the business. I would never work at your business unless I was absolutely desperate. Thankfully, I have never been that desperate.