Under the “Income” tab, hover over “Self-Employment” and then select “Business or Professional Activities” from the sub-menu. This will bring you to the “Your Self-Employment or Business Summary” page.
Click on “Edit” next to the business that you want to add the expenses to. On the “[NAME], review your self-employment income and expenses” page, click on “Business Expenses”. This will bring you to the “[NAME] let's look at your work expenses” page.
Click the blue “Continue” button until you reach the “[NAME], did you pay for utilities for a business property?” page. Here you can enter your telephone expenses. If you are using a mobile phone, remember to only enter the amount related to your business use. Ex: if you pay $100 per month for your cell phone service, but use it only 50% for business use, then you can claim only $50 of your monthly bill as a business expense.