How do you sync hearing aid to phone?

Depends on the hearing aid. Follow the steps in the hearing aid's own instructions to set them to pairing mode then look for them in Bluetooth settings on your iPhone.

Otherwise tell us what make and model of hearing Aids they are?

If they are specifically made for iPhone hearing aids see here: link-> Use Made for iPhone hearing devices - Apple Support

See here: https://www.hearinglife.com/hearing-aids/hearing-aid-repair-and-maintenance/self-help/oticon-accessories/pairing-oticon-opn-hearing-aids-with-apple-devices