View file app/Models/Antimat.php

<?php

namespace App\Models;

use Illuminate\Database\Capsule\Manager as DB;

class Antimat extends BaseModel
{
    /**
     * The table associated with the model.
     *
     * @var string
     */
    protected $table = 'antimat';

    /**
     * Indicates if the model should be timestamped.
     *
     * @var bool
     */
    public $timestamps = false;

    /**
     * The attributes that aren't mass assignable.
     *
     * @var array
     */
    protected $guarded = [];

    /**
     * Очищает строку от мата по базе слов
     *
     * @param  string $str строка
     * @return string      обработанная строка
     */
    public static function replace($str)
    {
        $words = self::query()
            ->orderBy(DB::raw('CHAR_LENGTH(string)'), 'desc')
            ->pluck('string')
            ->all();

        if ($words) {
            foreach($words as $word) {
                $str = preg_replace('|' . preg_quote($word) . '|iu', '***', $str);
            }
        }

        return $str;
    }
}