To hear with a hearing aid on the phone, hold the telephone near the hearing aid microphone, if you have a behind the ear hearing aid this will be behind your ear.
Phonak Audeo Belong B-312 (B50) Hearing Aid
The Audéo B family were created to simplify your life and make hearing effortless. Phonak says what makes Audéo B so special is its unique operating system called AutoSense OS. It senses your surroundings and adjusts your hearing aids every step of the way. All you have to do is turn them on, and the rest is automatic.