Although I know it can be a pain, I'd suggest two separate phones--or a clear understanding of what your employer's willingness to reimburse you means in regards to access to all of the information on your phone. Depending on the size of your employer, this may require a review of both HR and IT policies.

I work for the government, so anything on my work phone is subject to FOIA requests. As a result, no personal information, including personal texts, goes to my work phone. It sounds as if you probably don't work for the government, but your employer may feel they have a right to anything on the phone for which they reimburse you. Clarify that before making any decisions. Even there, I'd err on the side of caution and assume that if your employer ever felt the need, they'd try to access everything, both business and personal, on your phone.