You are a self-employed individual, you performed for the firm and invoice it, your employer pays for your service and gets deduction on operating expenses, you report income on your T1 according to the invoices, in which case you can deduct employment related expenses including telephone, cable, cell phone, part of autoexp, and toilet paper

perhaps your boss doesn't really know what's going on, and reject any T forms he offers, that's hard evidence that you want to avoid at all cost...