Port cannot be installed if PHP 7 is used because of the missing php70-mysql port. Probably the Makefile should be modified to chage the dependencies.
A commit references this bug: Author: jbeich Date: Mon Nov 7 04:28:15 UTC 2016 New revision: 425593 URL: https://svnweb.freebsd.org/changeset/ports/425593 Log: www/yourls: unbreak with lang/php70 to fix #56 Unknown extension mysql for PHP 70. PR: 214211 Submitted by: @zilon84 (via GitHub) Changes: head/www/yourls/Makefile