A SODIMM slot is a type of RAM slot (for SODIMMs: Small-Outline Dual Inline Memory Modules). If Task Manager says you have 1 RAM slot, it is correct. If Task Manager says you have 1 of 2 slots used but your SODIMM slot is empty, Task Manager is detecting your soldered RAM as a slot.
The word "port" implies an external connection to a peripheral device, whereas "slot" generally refers to an internal bus connection. For example, USB and Ethernet ports are sockets on the outside of the computer case that a cable plugs into.