How to make phone validation on form input?

Question

JavaScript

How to make validation on the form when entering or when inserting a record of this type into the form [phone] ?
at the output I want the form to display this type [phone] I

wrote such a validation.

validatePhone(event) {
        const { target } = event;
        const validatePhone = target.value.replace(/\D/g, '').match(/(\d{0,1})(\d{0,10})/);
        target.value = '+7'+validatePhone[2];
        this.formPhone.Phone = target.value = '+7'+validatePhone[2];
    }

This code cuts a lot when I insert it into the form [phone], then only +7999999 is displayed in the form