It depends how you're taxed, not how much you use the phone for work:
- Self-employed / sole trader / single-member LLC — Yes, but only the business-use share. On one phone used for both business and personal calls, you deduct the proportion of your actual use that is business, not the whole bill.
- Dedicated business line or second phone — The full cost. Nothing personal to apportion out, so there's no percentage to work out or defend. This is the cleanest position.
- W-2 employee, unreimbursed — Generally nothing on a US federal return. Unreimbursed employee expenses sat among the miscellaneous itemized deductions suspended under §67(g), and the One Big Beautiful Bill Act (P.L. 119-21) made that suspension permanent. Ask your employer about a reimbursement or stipend instead.
There is no standard percentage. Anyone quoting you one invented it. Work yours out by counting over a representative period — either minutes/calls, or days of use — pick one basis and stay consistent across the year. Changing it month to month to chase a bigger number is the pattern that fails a review.
The first-line trap (US landlines): IRC §262(b) treats any charge for basic local telephone service on the first telephone line provided to a residence as a personal expense — however much you work from home. A second residential line used for business isn't caught by it. This is a landline rule, separate from apportioning a mobile.
What's in scope: monthly plan/line rental, data and overage, business roaming. The handset may be an expense in the year you buy it or an asset written down over time, depending on cost and country — ask your accountant. Out of scope: personal streaming add-ons, family lines, insurance on a personal-only handset.
The record you need is two things: the bill (proves the amount) and the basis for your percentage (proves the business share). Twelve bills with no note explaining the split is half a record.
Where ExpenseBot fits: your carrier emails a bill every month, so connecting Gmail puts twelve months of them in a Google Sheet you own automatically. If your work mode is self-employed, Manage Expense Categories also has a Business % field per category — set it once and every expense in that category carries the business share through to your year-end report, which shows both the full amount and the calculated business portion. ExpenseBot does not decide your percentage; that judgement about your own usage stays yours.
⚠️ The IRS discontinued Publication 535, Business Expenses (last revision 2022). For general small-business deductions the current reference is Publication 334, Tax Guide for Small Business.
Full guide: Is My Phone Bill Tax Deductible?. For the general mechanic of splitting any mixed-use cost, see business use percentage. Same logic applies to your home office and your mileage. Estimates — confirm with your tax professional.