WooCommerce Phone Number Validation (+370/+371/+372) for LT/LV/EE

functions.php

// Add following code to functions php of your theme

add_action( 'woocommerce_checkout_process', 'validate_phone_number_for_specific_countries' );

function validate_phone_number_for_specific_countries() {
    $phone = isset( $_POST['billing_phone'] ) ? wc_clean( $_POST['billing_phone'] ) : '';
    $billing_country = isset( $_POST['billing_country'] ) ? wc_clean( $_POST['billing_country'] ) : '';

    // Specify the countries requiring phone number validation
    $countries_requiring_validation = array( 'LT', 'LV', 'EE' );

    // Proceed with validation if the billing country is one of the specified countries
    if ( in_array( $billing_country, $countries_requiring_validation ) ) {
        // Check if the phone number starts with '+' followed by digits
        if ( !preg_match( '/^\+\d+/', $phone ) ) {
            wc_add_notice( __( 'For Lithuania, Latvia, and Estonia, please enter a valid phone number with your country code. For example, +37012345678.', 'woocommerce' ), 'error' );
        }
    }
}