I don't know where and how should I use it. Can you please be more specific in the answer? I asked for solution related to xml view that can be changed using developer mode in the web interface. In case it is not possible this way please direct me to the tutorial where I can find detailed information. Thanks

Finally it works. Added foloowing related fields in file .../odoo/addons/project/models/project.py :

class Task(models.Model)

...

city = fields.Char('City', related='partner_id.city', readonly=True)

street = fields.Char('Street', related='partner_id.street', readonly=True)

phone = fields.Char('Phone', related='partner_id.phone', readonly=True)

...

Restart server, and use related field it in xml view editor of developer mode:

<field name="phone" />

...

Great but it is recommended to create a module for all the customization.