iphone 13 phone volume

After 16 months of performing satisfactorily, the speaker volume on phone calls is suddenly very low (barely audible). At the same time there is plenty of volume when playing music. This leads me to believe that the problem is not with the speaker but perhaps a software/settings problem. I have gone through and checked the settings to no avail. I did a factory reset and manually restored the phone, again this did not fix the problem. any help would be greatly appreciated. Thank you.