Just plug the Olympus TP-7 into the "MIC" jack of your recorder, and put the earphone side into your ear. When speaking on the telephone, the TP-7 will capture both sides of the conversation for recording on your voice recorder.
Olympus TP-7 Telephone Pickup Microphone (code 56298)
Supersensitive microphone for telephone conferencing. Comes with 2 plug adapters to convert either to 3.5 mm stereo plug or to a 2.5 mm monaural plug.
£14.68 (inc vat)