I’ve had the KS10 for about a week now, and phone calls on Bluetooth have been flawless, as they were for my KS9s. Never a complaint about callers not hearing me. I did see this Phonak Marvel 90 R Bluetooth Problem and Fix (changing a setting in the MyPhonak/Easyline app) as a possible fix to your problem, particularly with iPhones. My Pixel 4a (Android) has not had a problem with the KS9 or KS10.
I returned the Jabras after three weeks, because I preferred the Phonak approach to Bluetooth streaming, both in terms of audio quality and in terms of connectivity to laptops as well as phones. Jabras use Bluetooth LE for streaming, while Phonak uses Bluetooth classic. Jabras have much better battery life. My Jabra’s Bluetooth had its own frailties. There’s a discussion of the Jabras, including Bluetooth, here GN launching a Jabra branded M&RIE product at Costco - #221 by jim_lewis