How to display a list of countries in a form?

Question

PHP

It is necessary to display a list of countries in the form of filling Mobile phone.
here is a screen http://prntscr.com/gr4kf5
there is such a code

<form id="main-form" accept-charset="utf-8" onsubmit="formSubmit();" action="/" method="post" class="mfrm m_frm">
<div class="part part1 inl"><p class="namelabel">Ваше имя</p><input name="name" type="text" placeholder="Введите Ваше имя" required="" class="name f1_name"><input id="oneSignalID" name="oneSignalID" type="text" style="display: none;"></div>
    <div class="part part2 inl"><p class="namelabel">Ваш e-mail</p><input name="email" type="text" placeholder="Ваш Основной Email" required="" class="email f1_email"></div>        
        <div class="part part3 inl">
            <p class="namelabel" style="margin-left: 50px;">Ваш телефон</p>
        <div class="intl-tel-input allow-dropdown">
            <div class="flag-container">
                <div class="selected-flag" tabindex="0" title="Ukraine (Україна): +380">
                    <div class="iti-flag ua"/>
                    <div class="iti-arrow" style="left: 25px;"/>
                    </div>
</div>
</div>
    </div>   
        <input id="phone" class="phone" name="phone" required="" autocomplete="off" placeholder="[phone]" type="text"></div>

Answer 1

what is on the screen is
an alternative