Unable to install php5.6

/usr/local/directadmin/custombuild/tmp/tmp.2owsYaOBHt.php-5.6.40.tar.gz/ext/intl/intl_convertcpp.cpp: In function 'int intl_stringFromChar(icu_66::UnicodeString&, char*, int32_t, UErrorCode*)':
/usr/local/directadmin/custombuild/tmp/tmp.2owsYaOBHt.php-5.6.40.tar.gz/ext/intl/intl_convertcpp.cpp:35:2: error: 'UChar' was not declared in this scope
UChar *utf16 = ret.getBuffer(capacity);
^
/usr/local/directadmin/custombuild/tmp/tmp.2owsYaOBHt.php-5.6.40.tar.gz/ext/intl/intl_convertcpp.cpp:35:9: error: 'utf16' was not declared in this scope
UChar *utf16 = ret.getBuffer(capacity);
^
/usr/local/directadmin/custombuild/tmp/tmp.2owsYaOBHt.php-5.6.40.tar.gz/ext/intl/intl_convertcpp.cpp:35:21: error: 'class icu_66::UnicodeString' has no member named 'getBuffer'
UChar *utf16 = ret.getBuffer(capacity);
^
/usr/local/directadmin/custombuild/tmp/tmp.2owsYaOBHt.php-5.6.40.tar.gz/ext/intl/intl_convertcpp.cpp:40:9: error: 'u_strFromUTF8WithSub_66' was not declared in this scope
status);
^
/usr/local/directadmin/custombuild/tmp/tmp.2owsYaOBHt.php-5.6.40.tar.gz/ext/intl/intl_convertcpp.cpp: In function 'int intl_charFromString(const icu_66::UnicodeString&, char**, int*, UErrorCode*)':
/usr/local/directadmin/custombuild/tmp/tmp.2owsYaOBHt.php-5.6.40.tar.gz/ext/intl/intl_convertcpp.cpp:74:8: error: 'UChar' does not name a type
const UChar *utf16buf = from.getBuffer();
^
/usr/local/directadmin/custombuild/tmp/tmp.2owsYaOBHt.php-5.6.40.tar.gz/ext/intl/intl_convertcpp.cpp:76:54: error: 'utf16buf' was not declared in this scope
u_strToUTF8WithSub(*res, capacity - 1, &actual_len, utf16buf, from.length(),
^
make: *** [ext/intl/intl_convertcpp.lo] Error 1
make: *** Waiting for unfinished jobs....
*** The make has failed. Exiting...