I don’t think there’s any solution. Bluetooth headsets for phones go to great efforts to get only the voice of the person wearing the headset, and to filter out the noise around you. Hearing aids are the opposite, they are designed to receive sounds from all around the person, but not their own voice. It’s due the placement of the microphones and the directionality.
In simple terms, hearing aids are made to pick up sound from everywhere, and least of all from the person wearing them. For this reason, the person on the other end of your phone call will always hear background noise more than they will hear you speaking. You will need to find a quiet place in order to use the hearing aids as a phone headset.
I wish someone could make the hearing aids just work as the speaker part and use the microphone inside the phone. This may ro may not be possible, but I don’t think hearing aid users are enough of a market to get the phone manufacturers to create this feature.