When the little call window opens up on your computer does the switch to phone/PC button appear and does it respond if you click it?
Something else I changed was unrestricting the battery usage for phone link. I think by default it is set to optimised which means it may disconnect when not in use and perhaps by default disconnects when making a call to save battery. Which is fine ordinarily, but I'm able to keep my phone charged so isn't really an issue.