How to check if user exists in database given an email or a phone number in DRF

I need to check if a user exists in the database given their input: either their email or phone number. If the user exists, the user is used to take their order. If the user inputs both their email and phone and they don't exist in the database, I need to create the user. How do I do this?

This is the serializer:

class UserSerializer(serializers.ModelSerializer):
   
   class Meta:
       model = User
       fields = '__all__'
       extra_kwargs = {
           'email': {'required': True},
           'phone': {'required': True}
       }

   def create(self, validated_data):
       user= User.objects.create(
           email=validated_data['email'],
           phone=validated_data['phone']
       )

       user.save()

       return user


class OrderSerializer(serializers.ModelSerializer):
   food= FoodSerializer(many=True)

   class Meta:
       model = Order
       fields = ('date','food','phone','email')
       

       def validate(self, data):
           email = data.get('email')
           phone= data.get('phone')

           if not email and not phone:
               raise serializers.ValidationError("Email or phone required")

           return data  
               
       def checkuser(self, cliente, data):

           if data['email'] or data['phone'] in user:
               return user
           elif data['email'] or data['phone'] not in user:
               pass
                   
       def create(self, validated_data):
           order = Order.objects.create(
               email=validated_data['email'],
               phone=validated_data['phone'],
               date= validated_data['date'],
               food= validated_data['food'],
               quantity= validated_data['quantity'],
           )

           order.save()

           return order