api_call.php

//Microsoft Flow endpoint URL
$url='https://prod-44.westeurope.logic.azure.com:443/workflows/...';

//Data
$data = array(
  'jmeno'   => 'jmeno',
  'email'   => 'e-mail',
  'text'    => 'TEST'
);

$data_json = json_encode($data);                                                                                   

/* cURL Example */

$ch = curl_init($url);                                                                      
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");                                                                     
curl_setopt($ch, CURLOPT_POSTFIELDS, $data_json);                                                                  
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);                                                                      
curl_setopt($ch, CURLOPT_HTTPHEADER, array(                                                                          
    'Content-Type: application/json',                                                                                
    'Content-Length: ' . strlen($data_json))                                                                       
);                                                                                                                   
$result = curl_exec($ch);


/* file_get_contents() Example */

$options = array(

  'http' => array(
    'method'  => 'POST',
    'content' => $data_json,
    'header'=>  "Content-Type: application/json\r\n" .
                "Accept: application/json\r\n"
    )
);
$context  = stream_context_create( $options );
$result = file_get_contents( $url, false, $context );