iPhone 13 mini speakerphone not working in calls

I have a issue where I cannot be heard in speakerphone on calls. I have had my iPhone looked at by apple at the Genius Bar and the first time it was showing a hardware issue with the cell band technology. They replaced everything but the back ,the display and cameras. I continued to have the issue . I brought it back in and they said diagnostics came back clear this time. Both times they ruled out software. I don’t know what else to do because my phone is still messed up that I paid good money for .