Apple Watch cellular not working when iPhone is nearby.

I’ve had my Apple Watch series 8 as a family shared device for about a year with very few cellular problems. Just got an iPhone and restarted my watch to set it up with my phone, and now my cellular doesn’t work. I clicked “erase all data and keep plan” when prompted, and I checked my plan and I do have two cellular lines, one for each device. My problem is: I always have the little red x at the top of my Watch screen telling me no connection(unless I’m on Wi-Fi of course). But I go into settings and cellular, and then it immediately says that I’m connected and the x goes away, only to return after a few seconds when I exit the settings app. This happens all the time when my iPhone is Bluetooth paired to my watch, and only some of the time when I’m without my phone(or the bluetooth connection is disabled). I think my watch may be turning off cellular when it gets near my phone to conserve battery, which is fine, but even on a Bluetooth connection with the phone my watch can’t send or receive messages or do anything cellular. It’s like when it knows my phone is present, it just becomes useless cellular wise. Is this a feature or setting I can disable, should I talk to my service provider, or is there anything else I should try? Thanks.