While phpldapadmin requires php support, and returns an error on configure if php is not supported on the system, it does not depend on php.
I just checked, the unstable versions do correctly use the need_php4/5 functions, only the 0.9.8.2 version (stable x86) didn't. Now I fixed it and it correctly depends on dev-lang/php-4*, thanks for reporting this! Best regards, CHTEKK.