The AirPods work as they should on my iPhone and 18.2 bar the audiogram - functions and battery levels. They work as on my M1 MBP too, again bar the audiogram thing. The AirPods switch to the active devices as they should and battery levels are visible.
The custom audio set up on the iPad seems to be persistent unless you do a custom setup on the iPhone which will naturally overwrite it as one might expect.
All I’m missing is the supposed ability to use an audiogram to customise the audio on 18.2 like I can on the iPad on 18.0 - something which someone here reckons is possible. It isn’t AFAICS.
All 18.2 has done is activate the hearing test. Great! 8-(
It's not possible and won't be until the Hearing Aid feature is approved by the MHRA in the UK. At least your iPad is giving you the chance to use them and evaluate them to see if they will work for you. I never updated my iPhone and I'm happy to leave it on 17.7.1 for the time being.