How to insert link into php array?

Question

PHP

Hello everyone,
I made a telegram bot based on a video lesson from the Internet, which informs about applications from a site in a group.
There was such a question, now the phone number is in plain text, how to make it a link so that when you click on it, dialing opens?
I tried to insert the tag <a>, but the requests immediately stopped coming, i.e. everything broke
. The code itself

<?php
session_start();


$recepient = "*";



$token = "*";
$chat_id = "*";

$name = trim($_POST["user_name"]);
$phone = trim($_POST["user_phone"]);
$email = trim($_POST["user_email"]);
$form = trim($_POST["form_name"]);
$text = trim($_POST["user_message"]);

$browser=$_SERVER["HTTP_USER_AGENT"]; 
$refferer = $_SERVER['HTTP_REFERER'];
list($url) = explode('?', $_SERVER['HTTP_REFERER']);
$date = date("d.m.y", strtotime('+2 hour')); 
$time = date("H:i", strtotime('+2 hour'));

$arr = array(
'Форма:  ' => $form,
'Имя:  ' => $name,
'Телефон:  ' => $phone,
'Почта:  ' => $email,
'Сообщение:  ' => $text,
'Адресс страницы:  ' => $url,
'Дата:  ' => $date,
'Время:  ' => $time,

  );

foreach($arr as $key => $value) {
  $txt .= "<b>".$key."</b> ".$value."%0A";
};

$pagetitle = "Заявка с сайта";

$sendToTelegram = fopen("https://api.telegram.org/bot{$token}/sendMessage?chat_id={$chat_id}&parse_mode=html&text={$txt}","r");