Hi Ragav,

if your main goal is to validate field before saving record and raise validation error then you cam put your login into @api.constrains to achieve this.

When user click on save button then @api.constrains will execute and if number not on correct format then raise error.

But if you really want to make field as red like mandatory then you need to do the JS stuff to validate number and and make field border red using JS calculation.

There is an already module to validate number:

https://stackoverflow.com/questions/16135069/python-validation-mobile-number

https://apps.odoo.com/apps/modules/10.0/inputmask_widget/

Using JD:

https://stackoverflow.com/questions/26211225/validating-phone-numbers-using-javascript

Regards

Haresh Kansara