Throughout the security clearance investigation for a top secret clearance, will the investigators ever look at my personal emails, texts, or phone conversations?
There is nothing involved in any background investigation that entails looking at an applicants emails, texts, or phone calls. That would only be done as a part of an internal agency or company investigation for possible misconduct.
...unless...a reference or a neighbor brings up conduct and shows information speaking to the types of people you associate with. Then your investigator has to scope those aspects.