Whether a warrantless, post-arrest cell-phone-search is permissible under the Fourth-Amendment at the United-States-border

QUESTION PRESENTED FOR REVIEW Whether a warrantless, post-arrest cell phone search is permissible under the Fourth Amendment, simply because it takes place near the United States boundary with Mexico. In other words, does Riley v. California, 134 S. Ct. 2473 (2014), apply at the border? --prefix-