Two key questions:
A) You got a separate personal phone, was the work phone provided by the company?
B) Is mobile access an option or is it a required portion of your job?
The issue from the OP is that the company is requiring use of a smartphone, not providing a company phone (just a $45 subsidy that doesn't cover a full smartphone plan) and then requiring Airwatch to be used. This puts the employee in the position of either losing money to pay for a separate smartphone for work, or allowing their employer intrusive control and monitoring on their personal device.
This is a poor situation for the employee where they are forced to either give up privacy in their personal life or subsidize corporate savings from their own pocket.
A. Yes, the work phone is paid for fully by my company.
B. Since I am in an oncall rotation and considered "essential personnel" in emergency situations, mobile access is required.
Re: the bolded part, I entirely agree.
The OP's situation is certainly not fair but if that's what they require, I'm sure she knew that going into the job. The OP always has to option to move jobs if it's that upsetting to her/him.
I'm not trying to sound like an ass on this but some companies aren't always so generous to their employees. I'd be willing to bet that the OP's company decided to use Airwatch to help them be compliant with HIPAA laws, which is a whole other ball of wax!