> While the Supreme Court has long recognized a border-search exception to the Fourth Amendment’s warrant requirement, it applies to only two interests: promoting the duty regime and preventing contraband from entering the country; and ensuring that individuals are legally admitted.

The only reasons allowed for border searches are ensuring that individuals are legally admitted (inapplicable here because citizens are always legally entitled to enter) and preventing contraband from entering.

A wiped phone can't contain contraband, so wiping the phone serves the same purpose as a search. It's not destroying evidence anymore than throwing away a water bottle before going through TSA is destroying evidence.