The answer to this question depends on a number of factors, including the type of phone you have and the specific research and development activities that were undertaken. However, in general, you may be able to claim up to 100% of the cost of your phone, or even your monthly cell phone bill, as a business expense if it was used exclusively for telecommunications research and development purposes.
If you have any questions about whether you are eligible for a cell phone tax deduction, please consult with tax professionals for advice.