write contact form in wxPython?

Everyone will develop their own style when using wxPython. As Rolf has suggested, you do not just add widgets to a frame, but you need to add a panel. I have added a basic contact add screen below. The 'New' button creates an instance of a wx.Dialog, which captures the details of a contact. These are then available to the MainFrame where you can save them if you want.

Note that I have freely created new classes in the application to handle the different areas of concern. GUI apps can become very complex, and in my opinion, there is no substitute for factoring each bit of functionality into its own method or class.

Not everything needs to be a member of the frame class.

Note also the I have used sizers and not absolute positions.

This code does not do everything that you want to do, but it might help get you started.

import wx

BORDER = 5

class MainFrame(wx.Frame):
    def __init__(self, *args, **kwargs):
        super().__init__(None, *args, **kwargs)
        self.size = (400, 1000)
        self.Title = 'Contacts'
        self.Bind(wx.EVT_CLOSE, self.on_quit_click)

        self.panel = MainPanel(self)
        sizer = wx.BoxSizer(wx.VERTICAL)
        sizer.Add(self.panel)
        self.SetSizer(sizer)
        self.Center()
        self.Show()

    def new_contact(self, event):
        del event
        contact_add_screen = NewContact(self)
        try:
            contact_add_screen.ShowModal()
            if contact_add_screen.state == wx.ID_OK:
                print(contact_add_screen.first_name)
                print(contact_add_screen.last_name)
                # This is where you can save your contacts
        finally:
            contact_add_screen.Destroy()

    def on_quit_click(self, event):
        del event
        wx.CallAfter(self.Destroy)


class MainPanel(wx.Panel):
    """Create a panel class to contain screen widgets."""
    def __init__(self, parent, *args, **kwargs):
        super().__init__(parent, *args, **kwargs)

        self.parent = parent
        cmd_new_contact = wx.Button(self, id= wx.ID_NEW)
        cmd_new_contact.Bind(wx.EVT_BUTTON, parent.new_contact)
        sizer = wx.BoxSizer(wx.VERTICAL)
        sizer.Add(cmd_new_contact, flag=wx.ALL, border = BORDER)
        self.SetSizer(sizer)


class NewContact(wx.Dialog):
    def __init__(self, parent, *args, **kwargs):
        super().__init__(parent, *args, **kwargs)
        self.state = None
        self.first_name = None
        self.last_name = None
        self.parent = parent

        self.SetTitle('Add Contact')
        self.panel = ContactAddPanel(self)
        sizer = wx.BoxSizer()
        sizer.Add(self.panel)
        self.SetSizerAndFit(sizer)

    def on_cmd_save_click(self, event):
        del event
        self.first_name = self.panel.txt_first_name.GetValue()
        self.last_name = self.panel.txt_last_name.GetValue()
        self.state = wx.ID_OK
        self.Destroy()

    def on_quit_click(self, event):
        del event  # unused
        self.Destroy()



class ContactAddPanel(wx.Panel):
    TEXT_SIZE = (450, -1)

    def __init__(self, parent, *args, **kwargs):
        super().__init__(parent, *args, **kwargs)
        self.parent = parent

        contact_sizer = self._contact_sizer()
        button_panel = ButtonPanel(self, wx.ID_SAVE,
                                        self.parent.on_cmd_save_click,
                                        self.parent.on_quit_click)

        self.txt_first_name.SetFocus()

        sizer = wx.BoxSizer(wx.VERTICAL)
        sizer.Add(contact_sizer)
        sizer.Add(button_panel, flag=wx.EXPAND|wx.TOP, border=BORDER)
        main_sizer = wx.BoxSizer(wx.VERTICAL)
        main_sizer.Add(sizer, flag=wx.ALL, border=BORDER)
        self.SetSizer(main_sizer)

    def _contact_sizer(self):
        lbl_first_name= wx.StaticText(self, label='First name: ')
        self.txt_first_name= wx.TextCtrl(self, size=self.TEXT_SIZE)

        lbl_last_name = wx.StaticText(self, label='Last name:')
        self.txt_last_name = wx.TextCtrl(self, size=self.TEXT_SIZE)

        sizer = wx.GridBagSizer(BORDER, BORDER)
        sizer.Add(lbl_first_name, pos=(0, 0), flag=wx.ALIGN_RIGHT|wx.ALIGN_CENTER_VERTICAL)
        sizer.Add(self.txt_first_name, pos=(0, 1))
        sizer.Add(lbl_last_name, pos=(1, 0), flag=wx.ALIGN_RIGHT|wx.ALIGN_CENTER_VERTICAL)
        sizer.Add(self.txt_last_name, pos=(1, 1))
        return sizer


class ButtonPanel(wx.Panel):
    def __init__(self, parent, ok_id, ok_bind, cancel_bind, *args, **kwargs):
        super(ButtonPanel, self).__init__(parent, *args, **kwargs)
        self.cmd_action = wx.Button(self, ok_id)
        cmd_cancel = wx.Button(self, wx.ID_CANCEL)
        self.cmd_action.Bind(wx.EVT_BUTTON, ok_bind)
        cmd_cancel.Bind(wx.EVT_BUTTON, cancel_bind)

        sizer = wx.BoxSizer(wx.HORIZONTAL)
        sizer.Add(self.cmd_action)
        sizer.Add((0, 0), proportion=1)
        sizer.Add(cmd_cancel)
        self.SetSizer(sizer)

if __name__ == '__main__':
        wx_app = wx.App()
        MainFrame()
        wx_app.MainLoop()