The mobile phone policy is purely at the company's discretion. Some companies even include this as a part of CTC. Some companies outline this privilege based on the type of business function an employee is in, where the designation or levels are not considered. This is basically to address business needs.
The amounts are usually fixed based on the designation. Again, the cost of the device could be borne by the individual with prior approval of their Business Unit, and the same could be expensed, and so forth.
Overall, the company has to formulate the policy first to avoid any ambiguity.
Regards,
Ganesh Bhogadi