I'm having the same issue too while using Arctis 1 Wireless headphone (connected to the PC via 2.4GHz, not Bluetooth). I can hear the caller/receiver voice through my headset clearly, but they are not able to hear my voice. It was working fine previously while using Your Phone app (predecessor to Phone Link).
Both the headphone and the attached microphone are working fine in games, zoom, or google meet, so the problem must be with the Phone Link app.