The costs of a cell phone may be a business expense, but only the additional costs in using a cell phone for business are deductible. The Tax Court has several interesting cases on this. In one case, the taxpayer paid a flat rate on a phone used for business and personal calls. The court held that as he paid a flat rate for his personal phone and incurred no additional charges for business use, he has no deduction. (Ritchie, TC Summary Opinion 2005-181).
For an employee, if deductible, they would be entered as a miscellaneous itemized deduction for employee business expenses.
Example from Ritchie: "Petitioner’s cell phone was a personal phone that he also used for business calls. Petitioner testified that he paid a flat rate, regardless of phone usage. Therefore, aside from the personal expense of the phone, which is rendered nondeductible under § 262, he incurred no additional charge for business use."
If you are an employee, they are an employee business expense, which often results in no deduction anyway. You can claim them only if:
- You can itemize deductions, and
- they exceed 2% of your adjusted gross income.
If your miscellaneous itemized deductions clearly don't exceed 2% of your adjusted gross income there is no need to go through the time consuming effort to enter them. If they are over 2%, under the deductions and credits tab at the bottom of the list under other deductions and credits. Look for other deductions.
Turbotax explains the 2% rule at this site.
For employee business expenses look under Federal Taxes, then Deductions and Credits, then Explore on My Own, then Employment Expenses (near the bottom.)