Почему не отображается django select2?

поставил django-select2 по этой и этой инструкции, но select не показывает, в чем дело?

settings.py

INSTALLED_APPS = [
    ...
    'django_select2',
]

main urls.py

urlpatterns = [
    ...
    path('select2/', include('django_select2.urls')),
    ]

app models.py

class Clients(models.Model):
    name = models.CharField(max_length=150, blank=True)
    phone_regex = RegexValidator(regex=r'^\+?1?\d{9,15}$')
    phone = models.CharField(validators=[phone_regex], max_length=17)
 
    def __str__(self):
        return self.phone

app forms.py

class PhoneSelect2Widget(s2forms.ModelSelect2Widget):
    search_fields = ('phone__icontains',)
    queryset = Clients.objects.all()

class RelatedAddForm(forms.ModelForm):
    phone = forms.ModelChoiceField(
        widget=PhoneSelect2Widget,
        queryset=Clients.objects.all())

    def __init__(self, *args, **kwargs):
        self.request = kwargs.pop('request', None)
        super(RelatedAddForm, self).__init__(*args, **kwargs)
        self.fields['phone'].label = 'Телефон'

    class Meta:
        model = Clients
        fields = ['phone']