ASP.Net Core Razor Pages: Mobile Number (Cellphone Number) Validation using Data Annotations

Here Mudassar Khan has explained with an example, how to perform Mobile Number (Cellphone Number) TextBox validation i.e. exact Ten Numbers (Digits) validation on Client Side using Data Annotation in ASP.Net Core Razor Pages. The Mobile Phone Number (Cellphone Number) validation will be performed using Regular Expression (Regex).