Hi, and welcome to the Apple (user-to-user) Community!
Re: "Bluetooth connectivity issues with Phonak B90 Cros system on iPhone 15"
Sorry to hear your Hearing Aids are not connecting to your iPhone 15, using the updated app.
Am no expert in this area, yet your post to the community deserves some response.
You may want to check in the new app whether a firmware update for the Hearing Aids is available.
Else: If you have Hearing Aid documentation from Phonak, that may include advice on firmware updates.
Or: Perhaps your hearing specialist may know whether or not Phonak supplies firmware updates for compatibility.
You may want to enter your iPhone model into Phonak's compatibility webpage: to see what info & pairing advice is available online: https://www.phonak.com/en-int/support-options/phone-compatibility
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Re: My 15 doesn't even recognize them in bluetooth. Phonak says it should be able to.
If you haven't already:
✽ You can check in Settings > General > Software updates whether an iOS update is available for your iPhone:
(If so, it is wise to back up your iPhone data if you intend to update to the latest iOS version. (ie: iOS 18.2.1)
✽ Try turning Bluetooth off, wait a little, and then turn it back on.
✽ You can also check in iPhone: Settings > Accessibility > Hearing Devices > controls.
✽ If needed: Restart iPhone to re-establish the connection: (How to:Restart your iPhone - Apple Support)
✽ Bluetooth Trouble-shooting tips from Apple Support:
What to do: If you can't connect a Bluetooth accessory to your iPhone or iPad - Apple Support
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Re: "Made for iPhone" (Mfi) Hearing Aids
Apple support provides a long list of"Made for iPhone" Compatible Hearing Aids
Although a great many manufacture's models are listed, there are no Phonak Hearing Aids listed:
List of Made for iPhone hearing devices - Apple Support
✽ Tips for pairing and use: Use Made for iPhone hearing devices - Apple Support
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Re: Just wondering if there are any connectivity issues going around.
You are not alone in experiencing connectivity difficulties. Manufactures generally have online help available.
As Apple users, like yourself, we do not get to see whether any feedback is sent to Apple.
There are varying combinations of iPhone model, iOS version, hearing-aid model, app & firmware availability.
If needed: See a list of Apple phone numbers around the world
Contact Apple for support and service - Apple Support
All the best :-)