Hi garey16,
welcome to this Apple (user-to-user) Community!
Re: "receiving bluetooth signal from separate bluetooth transmitter"
Am no expert in this area, so I don't know whether or not the set-up you wish to use is achievable.
(Keeping the discussion-thread active may allow more opportunity for others with the know-how to reply.)
Just wondering whether using the iPhone as a microphone for the short-wave signal to reach your hearing-aids could be worth trying. See how to: Use Live Listen with Made for iPhone hearing devices - Apple Support
NB: Hearing-aids would likely need to be a "Made for iPhone: (Mfi) compatible model
Here's the List of Made for iPhone hearing devices - Apple Support
There's also an Apple support article online:
How to: Pair a third-party Bluetooth accessory with your iPhone or iPad - Apple Support