EIM32942 | Other expenses: telephone charges: payment package includes free calls
From HM Revenue & Customs · Employment Income Manual
Section 336 ITEPA 2003
No deduction is due for the cost of business calls if the terms on which the telephone is rented require the payment of a fixed sum to cover both line rental and calls. In such a case there is no cost that is wholly and exclusively attributable to the cost of a business call.