Phone expenses are deducted under Communication Expenses in the Self-Employment section. 

To do this once logged into your return click the following

• Tax Home
• Federal
• Wages and Income
• Scroll down and click Add More income
• See list of all income
• Click Show More next to Self-Employment
• Start next to Self-Employment
• As you walk through the entries you will be prompted to upgrade to Self-Employed in order to enter the expenses
• After clicking add expenses, select Communications and enter your cell phone bill.  

Remember, if you do not have a separate business line you must prorate your cell phone bill between business and personal usage.  You cannot deduct the entire bill.