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.
Oticon Siya CIC Hearing Aid
Oticon Siya Mini IIC is a Made for iPhone hearing aid with telecoil that amplifies the rich details of sounds, so they can focus in on every precious moment. The powerful Velox platform inside processes sound 50 times faster than the previous generation of hearing aids. This enables it to deliver excellent sound quality that helps improve speech understanding.