cannot hear conversation by holding the phone to my ear

stumped here

the earpiece on my phone all of a sudden stopped working proper, meaning, I had been able to hear conversations through the ear piece, now I have to use the speaker phone.

this phone had never been opened and I replaced the ear speaker and still having the same results with a muffled or obstructed ear piece speaker

so, could this be a burned out ribbon cable, could this be dust issue between the speaker and the screen

or worst case , is this a motherboard issue

thanks people