What drivers and or Libs control the phone app

im trying to diagnosis a specific problem with a the phone I just wanna know what driver or lib files control the phone in TW base roms also if you do know please be specific upon location thanks.Reason why I ask im trying to fix a port from a international rom I got everything to work but the phone it can make calls out and receive calls but i cannot hear them via speaker phone same goes for the mic . this is for the 910t