Converting java to php

public class argonpain {
  private String makeSixBits( String binaryStr ) {
    String ret = ""
    StringBuilder zeros = new StringBuilder ();
    int length = binaryStr.length();
    int appends = 6 - length ;
    for ( int i = 0; i < appends ; i ++) {
      zeros.append( "0"); // Append missing 0's to make expected bits
    }
    ret = zeros + binaryStr ;
    return ret ;
  }
}