Центрируется меню, при указании display flex

.header {
  display: flex;
}

<header class="header">
  <div class="container">
    <div class="header__block">
      <nav class="header__menu menu">
        <ul class="menu__list">
          <li class="menu__item">
            <a href="#" class="menu__link">Home</a>
          </li>
          <li class="menu__item">
            <a href="#" class="menu__link">Services</a>
          </li>
          <li class="menu__item">
            <a href="#" class="menu__link">About Us</a>
          </li>
          <li class="menu__item">
            <a href="#" class="menu__link">Our Clients</a>
          </li>
          <li class="menu__item">
            <a href="#" class="menu__link">Blog</a>
          </li>
          <li class="menu__item">
            <a href="#" class="menu__link">Contacts Us</a>
          </li>
        </ul>
      </nav>
      <div class="header__phone">
        <a href="" class="phone">Hotline: 89183170724</a>
      </div>
    </div>
  </div>
</header>