Q:

элементы друг над другом (flexbox)

Подскажите, пожалуйста, как можно разместить тел. номер над списком навигации? Код прилагается. Результат нужен как на картинке

* {
    box-sizing: border-box;
}
.flex {
    display: flex;
}
.grid {
    display: grid;
}
.textlocation {
    max-width: 1170px;
    margin: auto;
}
a {
    text-decoration: none;
}
header {
    position: relative;
    background-color: #1a1a1a;
    border-bottom: 3px solid #fc5700;
}
.firstpageheader {
}
.mainlogo {
    align-items: center;
    margin: 25px 0 25px 0;
}
.logotext {
    margin: 0;
    padding: 0 0 0 15px;
    line-height: 1.2em;
    color: white;
    font-family: 'Muli', sans-serif;
    font-weight: 300;
    font-size: 24px;
    text-transform: uppercase;
}
.commsword {
    font-size: 36px;
    font-weight: 800;
}
.mainNav {
    flex: 1;
    align-items: flex-end;
    justify-content: flex-end;
}
.mainNav ul {
    margin: 0;
    list-style-type: none;
}
.mainNav a { 
    font-family: 'Muli', sans-serif;
    font-weight: 600;
    font-size: 14px;
    color: white;
    padding-right: 40px;
    display: inline-block;
}
.mainNav a:last-child {
    padding-right: 0;
}
.mainNav li {
    border-bottom: 5px solid transparent;
    padding-bottom: 15px;
}
.mainNav li:hover {
    border-bottom: 5px solid #fc5700;
    padding-bottom: 15px;
}
.fa-phone {
    transform: rotate(90deg);
}
.phonenumber {
    font-family: 'Muli', sans-serif;
    font-weight: 800;
    font-size: 30px;
    color: #FFF;
}
<header>
    <div class="firstpageheader flex textlocation">
       
        <div class="mainlogo flex">
           <a href="" class="flex">
            <img src="img/logopic.png" class="mainlogopic">
            <p class="logotext">United<br> <span class="commsword">Comms</span></p></a>
        </div>
        <div class="mainNav flex">
            <p class="phonenumber"><i class="fas fa-phone"></i> (256) 152 3658</p>
            <ul>
                <a href=""><li>Home</li></a>
                <a href=""><li>Products</li></a>
                <a href=""><li>About Us</li></a>
                <a href=""><li>Services</li></a>
                <a href=""><li>Blog</li></a>
                <a href=""><li>Contact Us</li></a>
            </ul>
        </div>
    </div>
    </header>

A:

Codepen

* {
  box-sizing: border-box;
}

.flex {
  display: flex;
}

.grid {
  display: grid;
}

.textlocation {
  max-width: 1170px;
  margin: auto;
}

a {
  text-decoration: none;
}

header {
  position: relative;
  background-color: #1a1a1a;
  border-bottom: 3px solid #fc5700;
}

.firstpageheader {}

.mainlogo {
  align-items: center;
  margin: 25px 0 25px 0;
}

.logotext {
  margin: 0;
  padding: 0 0 0 15px;
  line-height: 1.2em;
  color: white;
  font-family: 'Muli', sans-serif;
  font-weight: 300;
  font-size: 24px;
  text-transform: uppercase;
}

.commsword {
  font-size: 36px;
  font-weight: 800;
}

.mainNav {
  flex: 1;
  align-items: flex-end;
  justify-content: flex-end;
  flex-direction: column;
}

.mainNav ul {
  margin: 0;
  list-style-type: none;
}

.mainNav a {
  font-family: 'Muli', sans-serif;
  font-weight: 600;
  font-size: 14px;
  color: white;
  padding-right: 40px;
  display: inline-block;
}

.mainNav a:last-child {
  padding-right: 0;
}

.mainNav li {
  border-bottom: 5px solid transparent;
  padding-bottom: 15px;
}

.mainNav li:hover {
  border-bottom: 5px solid #fc5700;
  padding-bottom: 15px;
}

.fa-phone {
  transform: rotate(90deg);
}

.phonenumber {
  font-family: 'Muli', sans-serif;
  font-weight: 800;
  font-size: 30px;
  color: #FFF;
}
<header>
  <div class="firstpageheader flex textlocation">

    <div class="mainlogo flex">
      <a href="" class="flex">
        <img src="img/logopic.png" class="mainlogopic">
        <p class="logotext">United<br> <span class="commsword">Comms</span></p>
      </a>
    </div>
    <div class="mainNav flex">
      <p class="phonenumber"><i class="fas fa-phone"></i> (256) 152 3658</p>
      <ul>
        <a href="">
          <li>Home</li>
        </a>
        <a href="">
          <li>Products</li>
        </a>
        <a href="">
          <li>About Us</li>
        </a>
        <a href="">
          <li>Services</li>
        </a>
        <a href="">
          <li>Blog</li>
        </a>
        <a href="">
          <li>Contact Us</li>
        </a>
      </ul>
    </div>
  </div>
</header>

