Convert a phone number into an HTML link

get_phone_number_link.php

<?php

/**
 * Create an HTML link using a phone number.
 * Supports international numbers by preserving common symbols.
 * Supports an optional extension displayed after the link.
 *
 * @param string $phone
 *
 * @return string
 */
function get_phone_number_link( $phone ) {
	// Check for an extension, split it from the phone number
	if ( preg_match('/([0-9])[^0-9]*(extension|ext|x).*?([0-9\-|\/]+)\b/i', $phone, $matches) ) {
		// Get extension to put after the link
		$extension = ' ext. ' . $matches[3];
		
		// Remove the extension from the phone number
		$pos = strpos( $phone, $matches[0] );
		$phone = substr( $phone, 0, $pos + 1 );
	}else{
		// No extension
		$extension = '';
	}
	
	// Get the digits
	$number = preg_replace('/[^0-9]/i', '', $phone); // "(123) 456-7890 ext. 123" => "1234567890"
	
	// Special formatting for USA
	if (preg_match('/^(\+1|1)?([2-9]\d{2})([\d]{3})([\d]{4})$/i', $number, $matches)) {
		//   555.123.1234 ->
		// (555) 456-7890 ->
		// = 1 (555) GET-LOST
		$link = sprintf('tel:+1%d%d%d', $matches[2], $matches[3], $matches[4]);
		$display = sprintf('1 (%d) %d-%d', $matches[2], $matches[3], $matches[4]);
	} else {
		// Other countries:
		// Only allow numbers and these symbols
		$link = 'tel:+' . $number;
		$display = preg_replace('/[^0-9\(\)\-\. ]/', '', $phone );
	}
	
	// Get an HTML link
	return sprintf(
		'<a href="%s" itemprop="telephone">%s</a>%s',
		esc_attr($link),
		esc_html($display),
		esc_html($extension)
	);
}