This plugin can be used for for easy phone number input when buying goods in Magento 2 with using flags of countries. Consist the option to set country automatically (using client IP) and phone number validation. To start extension work – you only need to install it. It’s really simple.

Also check WP eCommerce and WooCommerce versions of this plugin here:
WP eCommerce
WooCommerce

Features:

• Comfortable usability via admin panel
• Works with any Magento 2 theme
• Cross browser compatibility
• No coding required

v 1.0.2 - 01/06/2017
- Compatibility fix

v 1.0.1 - 02/12/2016
- Compatibility fix

v 1.0 - 26/08/2016
- First stable release