ResNet-50 has 4 bottleneck layers, which are represented by layer 1 to 4. Please check the paper on Resnet available at https://arxiv.org/pdf/1512.03385.pdf 6. And also refer, Class definition of ResNet in PyTorch available at https://github.com/pytorch/vision/blob/master/torchvision/models/resnet.py 8.
As pointed out by @ptrblck, softmax output should not be taken while training the network. It is used only in inference/validation.