Perhaps the employer would be willing to help you with the cost of a device to alert you to the phone.
How much are we talking here?
I would recommend if you don't have the financial means for a device that you contact
www.Modestneeds.com - I belong to this worthwhile group; they help you with one-time financial needs - send me a pm - if there is any problem.....dont give up a job you are good at and love.