Looks like your management are bunch of cheapskates. If I was offered stipend for use of my personal phone, it would have to cover the cost of calls, text and data for business use, and on top hefty monthly fee for wear and tear. If you want me to use my device, you rent it from me, so you need to pay for it.
Now the control of the data. Under no circumstances I would allow the company any access to my phone. They need to trust me with it, or they can pound sand, end of story.