Hi Ahmar,

You can use related fields for this.

define new field in sale order form as below: 

class SaleOrder(models.Model):
    _inherit = 'sale.order'
 
    customer_phone = fields.Char(related='partner_id.phone', string="Phone")

And in your xml, inherit the sale order model and add the new field

if you want to display the customer_phone field under customer try this:

Thank you