iPhone 8 call volume too quiet

When using the phone I cannot hear the other person unless I am somewhere with zero background noise (and even then it's quiet) or else I have to use speaker phone and hold it to my ear. My phone volume is turned all the way up. I made a call from my husband's 8 this am on the subway with his call volume at about 1/3 and could hear with no problem. I've tried suggested troubleshooting (restart, iOS is fully updated, turn bluetooth on/off, no screen protector, turn off/on phone noise cancellation) with no improvement. Has anyone been able to solve this without just needing a replacement phone?