Validating various input HTML forms

I'm looking for a review of my code for better design (to make sure it's more readable and legible).

<?php

// define variables and set to empty values
$nameErr = $phoneErr = $streetErr = $cityErr = $stateErr = $zipErr = "";
$name = $phone = $street = $city = $state = $zip = "";

// start script if the form is submitted
if ($_SERVER["REQUEST_METHOD"] == "POST") {

    if (empty($_POST["name"])) {
    $nameErr = "Name is required";
    }
    else {$name = test_input($_POST["name"]);
            // check if name only contains letters and whitespaces
        if (!preg_match("/^[a-zA-Z ]*$/",$name)) {
            $nameErr = "Only letters and white space allowed"; 
        }
}

    if (empty($_POST["phone"])) {
        $phoneErr = "Phone # is required";
    }
    else {$email = test_input($_POST["phone"]);
        // check if phone only contains numbers and dashes in correct format
        if (!preg_match("/^[0-9]{3}-[0-9]{3}-[0-9]{4}$/",$phone)) {
            $phoneErr = "Please resubmit Phone # in the following format: 555-     555-5555"; 
        }
    }

    if (empty($_POST["street"])) {
    $streetErr = "Address is required";
    }
    else {$street = test_input($_POST["street"]);
     // check if address syntax is valid
      if (!preg_match("/^[0-9a-zA-Z. ]+$/",$street)) {
       $streetErr = "Address appears to be invalid.";
      }
    }

    if (empty($_POST["city"])) {
      $cityErr = "City is required";
    }
    else {$city = test_input($_POST["city"]);
 // check if city syntax is valid
      if (!preg_match("/^[a-zA-Z ]*$/",$city)) {
      $cityErr = "City appears to be invalid." ; 
     }
    }

    if (empty($_POST["state"])) {
     $stateErr = "State is required";
} 
    else {$state = test_input($_POST["state"]);
 // check if state is valid uppercase abbv. and two letters
 if (!preg_match("/^(A[LKSZRAP]|C[AOT]|D[EC]|F[LM]|G[AU]|HI|I[ADL N]
     |K[SY]|LA|M[ADEHINOPST]|N[CDEHJMVY]|O[HKR]|P[ARW]|RI|S[CD] 
     |T[NX]|UT|V[AIT]|W[AIVY])$/",$state)) {
     $stateErr = "State appears to be invalid. (Hint...Use Upper-case!)" ; 
   }
}

if (empty($_POST["zip"])) {
    $zipErr = "Zip Code field is required";
} 
else {$zip = test_input($_POST["zip"]);
    // check if zip only contains numbers and dashes in correct format
    if (!preg_match("/^[0-9]{5}-[0-9]{4}$/",$phone)) {
        $phoneErr = "Please resubmit Zip Code in the following format: 55555-5555"; 
    }
}
}

function test_input($data) {
   $data = trim($data);
   $data = stripslashes($data);
   $data = htmlspecialchars($data);
   return $data;
}
?>