<?php

$fileStr         = file_get_contents(YOUR_PHP_FILE_PATH);
$fileContent     = "";
$commentTokens   = [T_COMMENT];
$commentTokens[] = defined('T_DOC_COMMENT') ? T_DOC_COMMENT : T_ML_COMMENT;

$tokens = token_get_all($fileStr);

foreach ($tokens as $token) {
    if (is_array($token)) {
        if (in_array($token[0], $commentTokens))
            continue;

        $token = $token[1];
    }

    $fileContent .= $token;
}