BlazorEditForms/Model/PhoneNumber.cs

using System.ComponentModel.DataAnnotations;

using FluentValidation;

namespace BlazorEditForms.Model;

public class PhoneNumber
{
    [Phone]
    public string Number { get; set; } = string.Empty;
    public PhoneNumberType Type { get; set; }
}

public class PhoneNumberValidator : AbstractValidator<PhoneNumber>
{
    public PhoneNumberValidator()
    {
        RuleFor(x => x.Number).NotEmpty().Matches(@"\+?\d+");
        RuleFor(x => x.Type).IsInEnum();
    }
}