Telephone
If your hearing aid is fitted with a Telephone Coil then switch to the T-coil position, your hearing aid will receive the sound from the telephone automatically.

If your hearing aid is not fitted with a T-coil, put the receiver close to your ear without pressing it against the ear. If you put your phone too close to your ear, the result of a hard reflective surface pressing against your ear and the hearing aid will result in feedback.

If you hear a whistling noise (feedback), change the position of the receiver until it stops. Find the result that is most successful for you.