i can`t determine why api.onchange wont work on my custom module. it does nothing when i change value of field phone

my code:

from openerp import models, fields, api, _

class crm_lead(models.Model):

_inherit = 'crm.lead'

 ************ my other inheritet or created methods ********

api.onchange('phone')

def onchange_make_change(self):

self.email_from = 'email@email.email'