Depending on the account types involved, and whether the transfers by telephone are made under a telephone transfer plan, the transfers may or may not be subject to Regulation E and therefore subject to the error resolution requirements of section 1005.11 of that regulation.
For example, if the accounts are business accounts, Regulation E won't apply. If the transfers are made by telephone, they may or may not be covered by the regulation, depending on information not supplied in your question. For further information, you can review the provisions of section 1005.3 of the regulation, which defines the term "electronic fund transfer," and explains which transactions are covered and which are not.