How to keep one country only or some countries in Phone no. Input

Add the below code in startup wiget controller

for India only 
ms.onlyCountries = ['IN']
ms.initialCountry = "IN"

for Saudi Arabia only 
ms.onlyCountries = ['SA']
ms.initialCountry = "SA"

for Multiple like both
ms.onlyCountries = ['IN', 'SA'] 

Put single or multiple country code you want to restrict on phone input