Where you are going is what I was also thinking in terms of certain components causing this. My idea is the phone.apk and telephony.apk(or similar name) are the phone parts. All of them? I really don't know. There may be more, but at least you can try this.
This Thread has a bunch of info on those files. I suggest reading all the comments to understand what to expect before you do it.
https://www.mobileread.com/forums/sho...ght=phone+file