phone call speaker

I have an iPhone 8 plus, Ive been having issues when I call because I can barely hear the other person, either I have to put it on speaker or use headphones to be able to hear clearly. Ive cleanse it several times I've also factory reset it because I though maybe I changed something and I forgot, but I went to the main store ant they said the only way to fix it was buying a new one and I am not going in that direction. I was wondering is there something I can do in other to fix the problem?