I have a 2-year-old iPhone XR in an OtterBox case, and my reception while sitting in my apartment is so bad that I can't have phone conversations at all. I can FaceTime, text, use Facebook video chat, etc., but I can't hold phone conversations because every other word is lost, and the ones I can hear are nearly incomprehensible. This seems to be the case regardless of whether I initiate or receive the call and regardless of whether I use Wi-Fi Calling or not. I've tried using my Apple wired earbuds, speakerphone, and normal hold-it-up-to-you-ear-until-your-arm-falls-asleep calling, with no apparent difference.
I live in a second-floor end apartment with one unit above me and one to the east, but the north, west, and south sides of the unit are unblocked by any other structures. It looks like my nearest cell tower is to the northwest. ZIP code is 99205 (Spokane, WA).
Any tips, tricks, or ideas are appreciated!