What is the equivalent of JavaScript's encodeURIcomponent in PHP?

Try rawurlencode. Or to be more precise:

function encodeURIComponent($str) {
    $revert = array('%21'=>'!', '%2A'=>'*', '%27'=>"'", '%28'=>'(', '%29'=>')');
    return strtr(rawurlencode($str), $revert);
}

This function works exactly how encodeURIComponent is defined:

encodeURIComponent escapes all characters except the following: alphabetic, decimal digits, - _ . ! ~ * ' ( )

Did you try urlencode ?

function encodeURIComponent($string) {
   $result = "";
   for ($i = 0; $i < strlen($string); $i++) {
      $result .= encodeURIComponentbycharacter(urlencode($string[$i]));
   }
   return $result;
}


function encodeURIComponentbycharacter($char) {
   if ($char == "+") { return "%20"; }
   if ($char == "%21") { return "!"; }
   if ($char == "%27") { return '"'; }
   if ($char == "%28") { return "("; }
   if ($char == "%29") { return ")"; }
   if ($char == "%2A") { return "*"; }
   if ($char == "%7E") { return "~"; }
   if ($char == "%80") { return "%E2%82%AC"; }
   if ($char == "%81") { return "%C2%81"; }
   if ($char == "%82") { return "%E2%80%9A"; }
   if ($char == "%83") { return "%C6%92"; }
   if ($char == "%84") { return "%E2%80%9E"; }
   if ($char == "%85") { return "%E2%80%A6"; }
   if ($char == "%86") { return "%E2%80%A0"; }
   if ($char == "%87") { return "%E2%80%A1"; }
   if ($char == "%88") { return "%CB%86"; }
   if ($char == "%89") { return "%E2%80%B0"; }
   if ($char == "%8A") { return "%C5%A0"; }
   if ($char == "%8B") { return "%E2%80%B9"; }
   if ($char == "%8C") { return "%C5%92"; }
   if ($char == "%8D") { return "%C2%8D"; }
   if ($char == "%8E") { return "%C5%BD"; }
   if ($char == "%8F") { return "%C2%8F"; }
   if ($char == "%90") { return "%C2%90"; }
   if ($char == "%91") { return "%E2%80%98"; }
   if ($char == "%92") { return "%E2%80%99"; }
   if ($char == "%93") { return "%E2%80%9C"; }
   if ($char == "%94") { return "%E2%80%9D"; }
   if ($char == "%95") { return "%E2%80%A2"; }
   if ($char == "%96") { return "%E2%80%93"; }
   if ($char == "%97") { return "%E2%80%94"; }
   if ($char == "%98") { return "%CB%9C"; }
   if ($char == "%99") { return "%E2%84%A2"; }
   if ($char == "%9A") { return "%C5%A1"; }
   if ($char == "%9B") { return "%E2%80%BA"; }
   if ($char == "%9C") { return "%C5%93"; }
   if ($char == "%9D") { return "%C2%9D"; }
   if ($char == "%9E") { return "%C5%BE"; }
   if ($char == "%9F") { return "%C5%B8"; }
   if ($char == "%A0") { return "%C2%A0"; }
   if ($char == "%A1") { return "%C2%A1"; }
   if ($char == "%A2") { return "%C2%A2"; }
   if ($char == "%A3") { return "%C2%A3"; }
   if ($char == "%A4") { return "%C2%A4"; }
   if ($char == "%A5") { return "%C2%A5"; }
   if ($char == "%A6") { return "%C2%A6"; }
   if ($char == "%A7") { return "%C2%A7"; }
   if ($char == "%A8") { return "%C2%A8"; }
   if ($char == "%A9") { return "%C2%A9"; }
   if ($char == "%AA") { return "%C2%AA"; }
   if ($char == "%AB") { return "%C2%AB"; }
   if ($char == "%AC") { return "%C2%AC"; }
   if ($char == "%AD") { return "%C2%AD"; }
   if ($char == "%AE") { return "%C2%AE"; }
   if ($char == "%AF") { return "%C2%AF"; }
   if ($char == "%B0") { return "%C2%B0"; }
   if ($char == "%B1") { return "%C2%B1"; }
   if ($char == "%B2") { return "%C2%B2"; }
   if ($char == "%B3") { return "%C2%B3"; }
   if ($char == "%B4") { return "%C2%B4"; }
   if ($char == "%B5") { return "%C2%B5"; }
   if ($char == "%B6") { return "%C2%B6"; }
   if ($char == "%B7") { return "%C2%B7"; }
   if ($char == "%B8") { return "%C2%B8"; }
   if ($char == "%B9") { return "%C2%B9"; }
   if ($char == "%BA") { return "%C2%BA"; }
   if ($char == "%BB") { return "%C2%BB"; }
   if ($char == "%BC") { return "%C2%BC"; }
   if ($char == "%BD") { return "%C2%BD"; }
   if ($char == "%BE") { return "%C2%BE"; }
   if ($char == "%BF") { return "%C2%BF"; }
   if ($char == "%C0") { return "%C3%80"; }
   if ($char == "%C1") { return "%C3%81"; }
   if ($char == "%C2") { return "%C3%82"; }
   if ($char == "%C3") { return "%C3%83"; }
   if ($char == "%C4") { return "%C3%84"; }
   if ($char == "%C5") { return "%C3%85"; }
   if ($char == "%C6") { return "%C3%86"; }
   if ($char == "%C7") { return "%C3%87"; }
   if ($char == "%C8") { return "%C3%88"; }
   if ($char == "%C9") { return "%C3%89"; }
   if ($char == "%CA") { return "%C3%8A"; }
   if ($char == "%CB") { return "%C3%8B"; }
   if ($char == "%CC") { return "%C3%8C"; }
   if ($char == "%CD") { return "%C3%8D"; }
   if ($char == "%CE") { return "%C3%8E"; }
   if ($char == "%CF") { return "%C3%8F"; }
   if ($char == "%D0") { return "%C3%90"; }
   if ($char == "%D1") { return "%C3%91"; }
   if ($char == "%D2") { return "%C3%92"; }
   if ($char == "%D3") { return "%C3%93"; }
   if ($char == "%D4") { return "%C3%94"; }
   if ($char == "%D5") { return "%C3%95"; }
   if ($char == "%D6") { return "%C3%96"; }
   if ($char == "%D7") { return "%C3%97"; }
   if ($char == "%D8") { return "%C3%98"; }
   if ($char == "%D9") { return "%C3%99"; }
   if ($char == "%DA") { return "%C3%9A"; }
   if ($char == "%DB") { return "%C3%9B"; }
   if ($char == "%DC") { return "%C3%9C"; }
   if ($char == "%DD") { return "%C3%9D"; }
   if ($char == "%DE") { return "%C3%9E"; }
   if ($char == "%DF") { return "%C3%9F"; }
   if ($char == "%E0") { return "%C3%A0"; }
   if ($char == "%E1") { return "%C3%A1"; }
   if ($char == "%E2") { return "%C3%A2"; }
   if ($char == "%E3") { return "%C3%A3"; }
   if ($char == "%E4") { return "%C3%A4"; }
   if ($char == "%E5") { return "%C3%A5"; }
   if ($char == "%E6") { return "%C3%A6"; }
   if ($char == "%E7") { return "%C3%A7"; }
   if ($char == "%E8") { return "%C3%A8"; }
   if ($char == "%E9") { return "%C3%A9"; }
   if ($char == "%EA") { return "%C3%AA"; }
   if ($char == "%EB") { return "%C3%AB"; }
   if ($char == "%EC") { return "%C3%AC"; }
   if ($char == "%ED") { return "%C3%AD"; }
   if ($char == "%EE") { return "%C3%AE"; }
   if ($char == "%EF") { return "%C3%AF"; }
   if ($char == "%F0") { return "%C3%B0"; }
   if ($char == "%F1") { return "%C3%B1"; }
   if ($char == "%F2") { return "%C3%B2"; }
   if ($char == "%F3") { return "%C3%B3"; }
   if ($char == "%F4") { return "%C3%B4"; }
   if ($char == "%F5") { return "%C3%B5"; }
   if ($char == "%F6") { return "%C3%B6"; }
   if ($char == "%F7") { return "%C3%B7"; }
   if ($char == "%F8") { return "%C3%B8"; }
   if ($char == "%F9") { return "%C3%B9"; }
   if ($char == "%FA") { return "%C3%BA"; }
   if ($char == "%FB") { return "%C3%BB"; }
   if ($char == "%FC") { return "%C3%BC"; }
   if ($char == "%FD") { return "%C3%BD"; }
   if ($char == "%FE") { return "%C3%BE"; }
   if ($char == "%FF") { return "%C3%BF"; }
   return $char;
}