Divi’s default contact form lacks the ability to add phone numbers etc.

This code, from here, allows you to match the same layout as the original contact form, when using CF7.

.wpcf7-text, .wpcf7-textarea, .wpcf7-captchar {
background-color: #eee !important;
border: none !important;
width: 100% !important;
-moz-border-radius: 0 !important;
-webkit-border-radius: 0 !important;
border-radius: 0 !important;
font-size: 14px;
color: #999 !important;
padding: 16px !important;
-moz-box-sizing: border-box;
-webkit-box-sizing: border-box;
box-sizing: border-box;
}
.wpcf7-submit {
color: #2EA3F2 !important;
margin: 8px auto 0;
cursor: pointer;
font-size: 20px;
font-weight: 500;
-moz-border-radius: 3px;
-webkit-border-radius: 3px;
border-radius: 3px;
padding: 6px 20px;
line-height: 1.7em;
background: transparent;
border: 2px solid;
-webkit-font-smoothing: antialiased;
-moz-osx-font-smoothing: grayscale;
-moz-transition: all 0.2s;
-webkit-transition: all 0.2s;
transition: all 0.2s;
}
.wpcf7-submit:hover { 
background-color: #eee; 
border-color:#eee; 
padding: 6px 20px !important; 
}