Hi,

Try the following code.

class ResPartner(models.Model):

    _inherit = 'res.partner'

    @api.constrains('phone')

    def _check_phone_length(self):

        for rec in self:

            if rec.phone:

                digits = re.sub(r'\D', '', rec.phone)  # Remove non-digit characters

                if len(digits) != 10:

                    raise ValidationError("Phone number must contain exactly 10 digits.")

- Removes all non-digit characters (so +966 55 344 8950 becomes 966553448950)

- Checks if the last 10 digits (i.e., local number) are exactly 10 digits long

- If not, raises a clear ValidationError

Hope it helps