If you want to textarea lines convert to array using php then check this demo code which help you.

Important thing that your textarea must need new line. In this code i added
for new line for better understand

$text = "Name:Jay <br/>
Email:jayviru@demo.com <br/>
Contact:9876541230";
$array_data = explode('<br/>', $text);

$final_data = array();
foreach ($array_data as $data){
    $format_data = explode(':',$data);
    $final_data[trim($format_data[0])] = trim($format_data[1]);
}
echo "<pre>";
print_r($final_data);

Then output is :

Array
(
    [Name] => Jay
    [Email] => jayviru@demo.com
    [Contact] => 9876541230
)

And if your text area value get using php variable then simple use this code

<?php
$text = $_POST['filed_value'];
$array_data = explode(PHP_EOL, $text);

$final_data = array();
foreach ($array_data as $data){
    $format_data = explode(':',$data);
    $final_data[trim($format_data[0])] = trim($format_data[1]);
}
echo "<pre>";
print_r($final_data);

This is get same value, if you face any problem then please inform me. I will try to help you